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‎Algorithms/Find_Target_Last_Index/findtargetlastindex.go

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package findtargetlastindex
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// RightBound, 有點類似 nums 大於 target的元素有幾個
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// 二分搜尋
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func Solution(nums []int, target int) int {
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left, right := 0, len(nums)-1
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for left <= right {
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mid := int(uint(left+right) >> 1)
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if nums[mid] == target {
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if nums[right] == target {
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return right
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} else {
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right--
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}
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} else if nums[mid] < target {
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left = mid + 1
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} else {
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right = mid - 1
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}
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}
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return -1
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}
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func SolutionRecursive(nums []int, target int) int {
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left, right := 0, len(nums)-1
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return findTarget(nums, left, right, target)
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}
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func findTarget(nums []int, left, right, target int) int {
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if left > right {
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return -1
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}
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mid := int(uint(left+right) >> 1)
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if nums[mid] == target {
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if nums[right] == target {
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return right
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} else {
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return findTarget(nums, mid, right-1, target)
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}
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} else if nums[mid] < target {
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return findTarget(nums, mid+1, right, target)
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} else {
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return findTarget(nums, left, mid-1, target)
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}
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}

‎Algorithms/Find_Target_Last_Index/findtargetlastindex.md

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---
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title: Find Target Last Index
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subtitle: ""
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date: 2023-11-16T17:09:00+08:00
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lastmod: 2023-11-16T17:09:00+08:00
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draft: false
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author: "Kimi.Tsai"
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authorLink: "https://kimi0230.github.io/"
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description: "在有序的array中 找出target在array中最後的index是什麼"
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license: ""
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images: []
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tags: [Interview, Algorithms, Go, Easy, Find Target Last Index, Right Bound, Left Bound]
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categories: [Algorithms]
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featuredImage: ""
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featuredImagePreview: ""
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hiddenFromHomePage: false
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hiddenFromSearch: false
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twemoji: false
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lightgallery: true
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ruby: true
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fraction: true
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fontawesome: true
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linkToMarkdown: false
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rssFullText: false
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toc:
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enable: true
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auto: true
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code:
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copy: true
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maxShownLines: 200
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math:
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enable: false
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# ...
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mapbox:
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# ...
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share:
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enable: true
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# ...
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comment:
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enable: true
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# ...
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library:
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css:
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# someCSS = "some.css"
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# located in "assets/"
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# Or
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# someCSS = "https://cdn.example.com/some.css"
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js:
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# someJS = "some.js"
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# located in "assets/"
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# Or
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# someJS = "https://cdn.example.com/some.js"
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seo:
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images: []
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# ...
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---
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# Find Target Last Index
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在有序的array中 找出target在array中最後的index是什麼
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用二分搜尋法去找, RightBound
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可參考
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https://github.com/kimi0230/LeetcodeGolang/blob/master/Leetcode/0704.Binary-Search/main.go
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---
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## 方法一
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```go
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func Solution(nums []int, target int) int {
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left, right := 0, len(nums)-1
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result := -1
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for left <= right {
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mid := int(uint(right+left) >> 1)
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if nums[mid] == target {
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// 繼續找, 縮小右邊
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if target == nums[right] {
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result = right
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break
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} else {
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right--
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}
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} else if nums[mid] < target {
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// 往右找
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left = mid + 1
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} else if nums[mid] > target {
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// 往左找
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right = mid - 1
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}
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}
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return result
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}
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```
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---
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## 方法二 遞迴
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```go
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func SolutionRecursive(nums []int, target int) int {
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left, right := 0, len(nums)-1
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return findTarget(nums, left, right, target)
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}
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func findTarget(nums []int, left, right, target int) int {
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if left > right {
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return -1
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}
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mid := int(uint(left+right) >> 1)
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if nums[mid] == target {
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if nums[right] == target {
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return right
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} else {
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return findTarget(nums, mid, right-1, target)
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}
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} else if nums[mid] < target {
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return findTarget(nums, mid+1, right, target)
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} else {
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return findTarget(nums, left, mid-1, target)
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}
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}
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```
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``` sh
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go test -benchmem -run=none LeetcodeGolang/Algorithms/Find_Target_Last_Index -bench=.
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goos: darwin
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goarch: amd64
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pkg: LeetcodeGolang/Algorithms/Find_Target_Last_Index
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cpu: Intel(R) Core(TM) i5-8259U CPU @ 2.30GHz
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BenchmarkSolution-8 54216429 24.75 ns/op 0 B/op 0 allocs/op
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BenchmarkSolutionRecursive-8 40756744 27.75 ns/op 0 B/op 0 allocs/op
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PASS
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ok LeetcodeGolang/Algorithms/Find_Target_Last_Index 2.537s
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```
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---
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## RightBound
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```go
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// 有點類似 nums 大於 target的元素有幾個
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func RightBound(nums []int, target int) (index int) {
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lenght := len(nums)
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if lenght <= 0 {
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return -1
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}
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left, right := 0, lenght-1
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for left <= right {
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// 除以2
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// mid := left + (right-left)>>1
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mid := int(uint(right+left) >> 1)
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if nums[mid] == target {
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// 注意:要繼續找右邊, 所以把左邊變大=mid+1
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left = mid + 1
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} else if nums[mid] < target {
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// 找右邊
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left = mid + 1
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} else if nums[mid] > target {
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// 找左邊
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right = mid - 1
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}
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}
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// 都沒找到 注意:right越界情況
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if right < 0 || nums[right] != target {
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return -1
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}
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return right
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}
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```
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## LeftBound
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``` go
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// 有點類似 nums 小於 target的元素有幾個
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func LeftBound(nums []int, target int) (index int) {
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lenght := len(nums)
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if lenght <= 0 {
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return -1
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}
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left, right := 0, lenght-1
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for left <= right {
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// 除以2
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// mid := left + (right-left)>>1
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mid := int(uint(right+left) >> 1)
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if nums[mid] == target {
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// 要繼續找左邊, 所以把右邊變小
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right = mid - 1
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} else if nums[mid] < target {
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// 找右邊
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left = mid + 1
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} else if nums[mid] > target {
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// 找左邊
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right = mid - 1
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}
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}
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// 都沒找到 注意: left越界情況
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if left >= lenght || nums[left] != target {
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return -1
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}
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return left
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}
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```

‎Algorithms/Find_Target_Last_Index/findtargetlastindex_test.go

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package findtargetlastindex
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import "testing"
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var tests = []struct {
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arg1 []int
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arg2 int
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want int
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}{
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{
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[]int{1, 2, 3, 4, 5, 6, 6, 6, 9},
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6,
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7,
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},
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{
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[]int{1, 2, 3, 4, 5, 5, 5, 6, 6, 6, 6, 6, 6, 7, 8, 9, 9, 9, 9},
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6,
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12,
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},
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{
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[]int{1, 2, 3, 4, 5, 5, 5, 6, 6, 6, 6, 6, 6, 7, 8, 9, 9, 9, 9},
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5,
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6,
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},
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{
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[]int{5, 7, 7, 8, 8, 10},
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8,
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4,
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},
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{
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[]int{5, 7, 7, 8, 8, 10},
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6,
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-1,
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},
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{
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[]int{1, 2, 3, 4, 5},
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3,
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2,
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},
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{
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[]int{1, 2, 3, 4, 5},
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5,
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4,
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},
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{[]int{1, 2, 3, 4, 5},
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0,
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-1,
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},
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}
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func TestSolution(t *testing.T) {
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for _, tt := range tests {
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if got := Solution(tt.arg1, tt.arg2); got != tt.want {
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t.Errorf("got = %v, want = %v", got, tt.want)
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}
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}
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}
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func TestSolutionRecursive(t *testing.T) {
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for _, tt := range tests {
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// start := 0
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// end := len(tt.arg1) - 1
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if got := SolutionRecursive(tt.arg1, tt.arg2); got != tt.want {
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t.Errorf("got = %v, want = %v", got, tt.want)
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}
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// SolutionRecursive(tt.arg1, start, end, tt.arg2)
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}
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}
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func BenchmarkSolution(b *testing.B) {
72+
b.ResetTimer()
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for i := 0; i < b.N; i++ {
74+
for _, tt := range tests {
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Solution(tt.arg1, tt.arg2)
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}
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}
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}
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func BenchmarkSolutionRecursive(b *testing.B) {
80+
b.ResetTimer()
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for i := 0; i < b.N; i++ {
82+
for _, tt := range tests {
83+
SolutionRecursive(tt.arg1, tt.arg2)
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}
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}
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}
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/*
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go test -benchmem -run=none LeetcodeGolang/Algorithms/Find_Target_Last_Index -bench=.
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goos: darwin
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goarch: amd64
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pkg: LeetcodeGolang/Algorithms/Find_Target_Last_Index
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cpu: Intel(R) Core(TM) i5-8259U CPU @ 2.30GHz
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BenchmarkSolution-8 54216429 24.75 ns/op 0 B/op 0 allocs/op
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BenchmarkSolutionRecursive-8 40756744 27.75 ns/op 0 B/op 0 allocs/op
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PASS
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ok LeetcodeGolang/Algorithms/Find_Target_Last_Index 2.537s
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*/

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