feat: leetcode 398

Author: deweyou

README.md

@@ -2,7 +2,7 @@
 
 <p align="center">
 <!-- TOPICS COUNT START -->
-<img src="https://img.shields.io/badge/-进度:333-green" alt="进度:333">
+<img src="https://img.shields.io/badge/-进度:334-green" alt="进度:334">
 <!-- TOPICS COUNT END -->
 <a href="./assets/docs/TOPICS.md"><img src="https://img.shields.io/badge/-题库目录-blue" alt="题库目录"></a>
 <a href="./assets/docs/CATEGORIES.md"><img src="https://img.shields.io/badge/-题库分类-red" alt="题库分类"></a>

assets/data/categories.json

@@ -176,6 +176,12 @@
         "path": "./problemset/insert-delete-getrandom-o1/README.md",
         "difficulty": "中等"
       },
+      {
+        "id": "398",
+        "title": "随机数索引",
+        "path": "./problemset/random-pick-index/README.md",
+        "difficulty": "中等"
+      },
       {
         "id": "432",
         "title": "全 O(1) 的数据结构",
@@ -1571,6 +1577,12 @@
         "path": "./problemset/utf-8-validation/README.md",
         "difficulty": "中等"
       },
+      {
+        "id": "398",
+        "title": "随机数索引",
+        "path": "./problemset/random-pick-index/README.md",
+        "difficulty": "中等"
+      },
       {
         "id": "420",
         "title": "强密码检验器",

assets/data/topics.json

@@ -2579,6 +2579,16 @@
     "url": "https://leetcode-cn.com/problems/rotate-function/",
     "path": "./problemset/rotate-function/README.md"
   },
+  {
+    "id": "398",
+    "title": {
+      "cn": "随机数索引",
+      "en": "random-pick-index"
+    },
+    "difficulty": "中等",
+    "url": "https://leetcode-cn.com/problems/random-pick-index/",
+    "path": "./problemset/random-pick-index/README.md"
+  },
   {
     "id": "420",
     "title": {
@@ -3329,4 +3339,4 @@
     "url": "https://leetcode-cn.com/problems/sum-of-subarray-ranges/",
     "path": "./problemset/sum-of-subarray-ranges/README.md"
   }
-]
+]

assets/docs/CATEGORIES.md

@@ -33,6 +33,7 @@
 | 290. [单词规律](../../problemset/word-pattern/README.md) | 简单 |
 | 355. [设计推特](../../problemset/design-twitter/README.md) | 中等 |
 | 380. [O(1) 时间插入、删除和获取随机元素](../../problemset/insert-delete-getrandom-o1/README.md) | 中等 |
+| 398. [随机数索引](../../problemset/random-pick-index/README.md) | 中等 |
 | 432. [全 O(1) 的数据结构](../../problemset/all-one-data-structure/README.md) | 困难 |
 | 599. [两个列表的最小索引总和](../../problemset/minimum-index-sum-of-two-lists/README.md) | 简单 |
 | 653. [两数之和 IV - 输入 BST](../../problemset/two-sum-iv-input-is-a-bst/README.md) | 简单 |
@@ -303,6 +304,7 @@
 | 307. [ 区域和检索 - 数组可修改](../../problemset/range-sum-query-mutable/README.md) | 中等 |
 | 310. [最小高度树](../../problemset/minimum-height-trees/README.md) | 中等 |
 | 393. [UTF-8 编码验证](../../problemset/utf-8-validation/README.md) | 中等 |
+| 398. [随机数索引](../../problemset/random-pick-index/README.md) | 中等 |
 | 420. [强密码检验器](../../problemset/strong-password-checker/README.md) | 困难 |
 | 521. [最长特殊序列](../../problemset/longest-uncommon-subsequence/README.md) | 简单 |
 | 537. [复数乘法](../../problemset/complex-number-multiplication/README.md) | 中等 |

assets/docs/TOPICS.md

@@ -516,6 +516,8 @@
 
 [396. 旋转函数](../../problemset/rotate-function/README.md)
 
+[398. 随机数索引](../../problemset/random-pick-index/README.md)
+
 [420. 强密码检验器](../../problemset/strong-password-checker/README.md)
 
 [429. N 叉树的层序遍历](../../problemset/n-ary-tree-level-order-traversal/README.md)

problemset/random-pick-index/README.md

@@ -0,0 +1,95 @@
+# 随机数索引
+
+> 难度：中等
+>
+> https://leetcode-cn.com/problems/random-pick-index/
+
+## 题目
+
+给定一个可能含有重复元素的整数数组，要求随机输出给定的数字的索引。 您可以假设给定的数字一定存在于数组中。
+
+注意：数组大小可能非常大。 使用太多额外空间的解决方案将不会通过测试。
+
+### 示例:
+
+```
+int[] nums = new int[] {1,2,3,3,3};
+Solution solution = new Solution(nums);
+
+// pick(3) 应该返回索引 2,3 或者 4。每个索引的返回概率应该相等。
+solution.pick(3);
+
+// pick(1) 应该返回 0。因为只有nums[0]等于1。
+solution.pick(1);
+```
+
+## 解题
+
+### 哈希表
+
+```ts
+/**
+ * 哈希表
+ */
+export class Solution {
+  indexMap = new Map<number, number[]>()
+
+  /**
+   * @desc 时间复杂度 O(N)  空间复杂度 O(N)
+   * @param nums
+   */
+  constructor(nums: number[]) {
+    for (let i = 0; i < nums.length; i++) {
+      const num = nums[i]
+      if (this.indexMap.has(num))
+        this.indexMap.get(num)!.push(i)
+      else
+        this.indexMap.set(num, [i])
+    }
+  }
+
+  /**
+   * @desc 时间复杂度 O(1)  空间复杂度 O(N)
+   * @param nums
+   */
+  pick(target: number): number {
+    const idxs = this.indexMap.get(target)
+    if (!idxs) return -1
+    if (idxs.length === 1) return idxs[0]
+
+    return idxs[(Math.random() * idxs.length) >> 0]
+  }
+}
+```
+
+### 水塘抽样
+
+```ts
+/**
+ * 水塘抽样
+ */
+export class Solution2 {
+  /**
+   * @desc 时间复杂度 O(1)  空间复杂度 O(1)
+   * @param nums
+   */
+  constructor(public nums: number[]) {}
+
+  /**
+   * @desc 时间复杂度 O(N)  空间复杂度 O(1)
+   * @param nums
+   */
+  pick(target: number): number {
+    let ans = 0
+    for (let i = 0, cnt = 0; i < this.nums.length; i++) {
+      if (this.nums[i] === target) {
+        // 记录target的次数
+        cnt++
+        if ((Math.random() * cnt) >> 0 === 0) ans = i
+      }
+    }
+
+    return ans
+  }
+}
+```

problemset/random-pick-index/index.spec.ts

@@ -0,0 +1,11 @@
+import { expect, it } from 'vitest'
+import { Solution, Solution2 } from '.'
+
+it.each([
+  ['哈希表', Solution],
+  ['水塘抽样', Solution2],
+])('随机数索引：%s', (_, Ctor) => {
+  const solution = new Ctor([1, 2, 3, 3, 3])
+  expect(solution.pick(3)).toMatch(/2|3|4/)
+  expect(solution.pick(1)).toBe(0)
+})

problemset/random-pick-index/index.ts

@@ -0,0 +1,60 @@
+/**
+ * 哈希表
+ */
+export class Solution {
+  indexMap = new Map<number, number[]>()
+
+  /**
+   * @desc 时间复杂度 O(N)  空间复杂度 O(N)
+   * @param nums
+   */
+  constructor(nums: number[]) {
+    for (let i = 0; i < nums.length; i++) {
+      const num = nums[i]
+      if (this.indexMap.has(num))
+        this.indexMap.get(num)!.push(i)
+      else
+        this.indexMap.set(num, [i])
+    }
+  }
+
+  /**
+   * @desc 时间复杂度 O(1)  空间复杂度 O(N)
+   * @param nums
+   */
+  pick(target: number): number {
+    const idxs = this.indexMap.get(target)
+    if (!idxs) return -1
+    if (idxs.length === 1) return idxs[0]
+
+    return idxs[(Math.random() * idxs.length) >> 0]
+  }
+}
+
+/**
+ * 水塘抽样
+ */
+export class Solution2 {
+  /**
+   * @desc 时间复杂度 O(1)  空间复杂度 O(1)
+   * @param nums
+   */
+  constructor(public nums: number[]) {}
+
+  /**
+   * @desc 时间复杂度 O(N)  空间复杂度 O(1)
+   * @param nums
+   */
+  pick(target: number): number {
+    let ans = 0
+    for (let i = 0, cnt = 0; i < this.nums.length; i++) {
+      if (this.nums[i] === target) {
+        // 记录target的次数
+        cnt++
+        if ((Math.random() * cnt) >> 0 === 0) ans = i
+      }
+    }
+
+    return ans
+  }
+}