原题
给定一个按照升序排列的整数数组nums
,和一个目标值target
。找出给定目标值在数组中的开始位置和结束位置。
你的算法时间复杂度必须是 O(log n) 级别。
如果数组中不存在目标值,返回 [-1, -1]
。
示例 1:
输入: nums = [5,7,7,8,8,10], target = 8输出: [3,4]
示例 2:
输入: nums = [5,7,7,8,8,10], target = 6输出: [-1,-1]
用二分查找找到目标数的左边界和有边界
public int[] searchRange(int[] nums, int target) {return new int[]{left_bound(nums,target),right_bound(nums,target)};}public int left_bound(int[] nums, int target) {int low = 0, high = nums.length - 1;while (low <= high) {int middle = low + (high - low) / 2;if (nums[middle] > target) {high = middle - 1;} else if (nums[middle] < target) {low = middle + 1;} else {high = middle - 1;}}//检查出界情况if (low > nums.length -1 || nums[low] != target) {return -1;}return low;}public int right_bound(int[] nums, int target) {int low = 0, high = nums.length - 1;while (low <= high) {int middle = low + (high - low) / 2;if (nums[middle] > target) {high = middle - 1;} else if (nums[middle] < target) {low = middle + 1;} else {low = middle + 1;}}if(high < 0 || nums[low]!=target){return -1;}return high;}