update

Author: ntduan

README.md

@@ -23,9 +23,16 @@
 ##### [Contains-Duplicate](./leetcode/Contains-Duplicate.ts)
 ##### [Rotate-Array](./leetcode/Rotate-Array.ts)
 ##### [Single-Number](./leetcode/Single-Number.ts)
-##### [Intersection-of-Two-Arrays-II](./leetcode/Intersection-of-Two-Arrays-II.ts)
+##### **[Intersection-of-Two-Arrays-II](./leetcode/Intersection-of-Two-Arrays-II.ts)**
 ##### [Plus-One](./leetcode/Plus-One.ts)
 ##### [Move-Zeroes](./leetcode/Move-Zeroes.ts)
+##### [Two-Sum](./leetcode/Two-Sum.ts)
+##### [Find-the-Duplicate-Number](./leetcode/Find-the-Duplicate-Number.ts) ？？
+##### [Find-Pivot-Index](./leetcode/Find-Pivot-Index.ts)
+
+## 字符串
+##### [Shortest-Distance-to-a-Character](./leetcode/Shortest-Distance-to-a-Character.ts)
+
 
 ## 双指针
 ##### [remove-duplicates-from-sorted-array](./leetcode/Remove-Duplicates-from-Sorted-Array.ts)

leetcode/Find-Pivot-Index.ts

@@ -0,0 +1,16 @@
+/**
+ * https://leetcode.com/problems/find-pivot-index/description/
+*/
+
+/**
+ * 先求出总和，然后遍历累加的左边的和，用总和减去当前值和左边的和就右边的和，比较他们的值。
+*/
+const pivotIndex = (nums: number[]): number => {
+  const totalSum = nums.reduce((a, b) => a + b)
+  let leftSum = 0
+  for(let i = 0; i < nums.length; i++) {
+    if(leftSum === totalSum - nums[i]) return i
+    leftSum += nums[i]
+  }
+  return -1
+};

leetcode/Find-the-Duplicate-Number.ts

@@ -0,0 +1,30 @@
+/**
+ * https://leetcode.com/problems/find-the-duplicate-number/description/
+ */
+
+/**
+ * 暴力查找
+ */
+// const findDuplicate = (nums: number[]): number => {
+//   for (let i = 0; i < nums.length; i++) {
+//     for (let j = i + 1; j < nums.length; j++) {
+//       if (nums[j] === nums[i]) return nums[j];
+//     }
+//   }
+//   return Number.MIN_SAFE_INTEGER;
+// };
+
+/**
+ * 排序，略
+*/
+
+/**
+ * hash表，略
+*/
+
+/**
+ * https://leetcode.com/problems/find-the-duplicate-number/solution/?page=2
+ * Floyd's Tortoise and Hare (Cycle Detection)
+*/
+
+//@TODO

leetcode/Intersection-of-Two-Arrays-II.ts

@@ -7,7 +7,7 @@
  * 定义一个空数组，然后遍历 nums2, 如果 nums2 中的值在哈希表中存在，且数量大于 0 ，则将这个 key 推入 result 中。数量 -1。
  */
 // const intersect = (nums1: number[], nums2: number[]): number[] => {
-//   const intersectMap = new Map();
+//   const intersectMap = {};
 //   for (let i = 0; i < nums1.length; i++) {
 //     intersectMap[nums1[i]] = (intersectMap[nums1[i]] || 0) + 1;
 //   }

leetcode/Shortest-Distance-to-a-Character.ts

@@ -0,0 +1,46 @@
+/**
+ * https://leetcode.com/problems/shortest-distance-to-a-character/description/
+ */
+
+/**
+ * 遍历得到目标c的位置。
+ * 在遍历，求出每一点到c的距离中的最小值。
+ */
+// const shortestToChar = (S: string, C: string) => {
+//   const result = [];
+//   const targetIndex = [];
+//   for (let i = 0; i < S.length; i++) {
+//     if (S[i] === C) targetIndex.push(i);
+//   }
+//   for (let j = 0; j < S.length; j++) {
+//     const minD = targetIndex.reduce((result, index) => {
+//       result = Math.min(Math.abs(index - j), result);
+//       return result;
+//     }, Number.MAX_SAFE_INTEGER);
+//     result[j] = minD;
+//   }
+//   return result;
+// };
+
+/**
+ * “loveleetcode”
+ * 从左到右遍历一遍，得到该位置到最近的左边的 c 的距离。[0, 0, 0, 3, 1, 5, 6, 1, 2, 3, 4, 11]
+ * 再从右到左遍历一遍，得到该位置到最近的右边的 c 的距离, 求左边距离和右边距离中的最小值
+ */
+const shortestToChar = (S: string, C: string) => {
+  const result = [];
+
+  let leftPosition = Number.MIN_SAFE_INTEGER;
+  for (let i = 0; i < S.length; i++) {
+    if (S[i] === C) leftPosition = i;
+    result[i] = i - leftPosition;
+  }
+
+  let rightPosition = Number.MAX_SAFE_INTEGER;
+  for (let i = S.length - 1; i >= 0; i--) {
+    if (S[i] === C) rightPosition = i;
+    result[i] = Math.min(rightPosition - i, result[i]);
+  }
+
+  return result;
+};

leetcode/Two-Sum.ts

@@ -0,0 +1,34 @@
+/**
+ * https://leetcode.com/problems/two-sum/description/
+ */
+
+/**
+ * 使用 map，然后找到 tartget - nums[i] 是否存在
+ */
+const twoSum = function(nums: number[], target: number): number[] {
+  const numsMap = new Map();
+  for (let i = 0; i < nums.length; i++) {
+    if (nums[i] > target) continue
+    if (numsMap.has(target - nums[i])) return [numsMap.get(target - nums[i]), i];
+    numsMap.set(nums[i], i);
+  }
+  return [-1, -1];
+};
+
+/**
+ * 如果数组是已排序的，双指针向中间靠拢
+ */
+
+// const twoSum = function(nums: number[], target: number): number[] {
+//   let [i, j] = [0, nums.length - 1];
+//   while (j > i) {
+//     const sum = nums[i] + nums[j];
+//     if (sum > target) {
+//       j--;
+//     } else if (sum < target) {
+//       i++;
+//     } else {
+//       return [i, j];
+//     }
+//   }
+// };