一、寻找一个数（最基本的二分搜索）

  1. int binarySearch(int[] nums, int target) {
  2.     int left = 0; 
  3.     int right = nums.length - 1; // 注意
  5.     while(left <= right) { // 注意
  6.         int mid = (right + left) / 2;
  7.         if(nums[mid] == target)
  8.             return mid; 
  9.         else if (nums[mid] < target)
  10.             left = mid + 1; // 注意
  11.         else if (nums[mid] > target)
  12.             right = mid - 1; // 注意
  13.         }
  14.     return -1;
  15. }

二、寻找左侧边界的二分搜索

  1. int left_bound(int[] nums, int target) {
  2.     if (nums.length == 0) return -1;
  3.     int left = 0;
  4.     int right = nums.length; // 注意
  6.     while (left < right) { // 注意
  7.         int mid = (left + right) / 2;
  8.         if (nums[mid] == target) {
  9.             right = mid;
  10.         } else if (nums[mid] < target) {
  11.             left = mid + 1;
  12.         } else if (nums[mid] > target) {
  13.             right = mid; // 注意
  14.         }
  15.     }
  16.     return left;
  17. }

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三、寻找右侧边界的二分查找

  1. int right_bound(int[] nums, int target) {
  2.     if (nums.length == 0) return -1;
  3.     int left = 0, right = nums.length;
  5.     while (left < right) {
  6.         int mid = (left + right) / 2;
  7.         if (nums[mid] == target) {
  8.             left = mid + 1; // 注意
  9.         } else if (nums[mid] < target) {
  10.             left = mid + 1;
  11.         } else if (nums[mid] > target) {
  12.             right = mid;
  13.         }
  14.     }
  15.     return left - 1; // 注意