力扣labuladong——一刷day24

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前言

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一文搞懂二分查找，左闭右闭，或者左闭右开，以及寻找左右边界

一、力扣34. 在排序数组中查找元素的第一个和最后一个位置

class Solution {
    public int[] searchRange(int[] nums, int target) {
        int[] res = new int[]{-1,-1};
        int left = 0, right = nums.length-1;
        while(left <= right){
            int mid = left + (right-left)/2;
            if(nums[mid] == target){
                right = mid-1;
            }else if(nums[mid] > target){
                right = mid -1;
            }else{
                left = mid+1;
            }
        }
        if(left >= 0 && left <= nums.length-1){
            res[0] = nums[left] == target ? left : -1;
        }
        left = 0; right = nums.length-1;
        while(left <= right){
            int mid = left + (right-left)/2;
            if(nums[mid] == target){
                left = mid+1;
            }else if(nums[mid] > target){
                right = mid -1;
            }else{
                left = mid + 1;
            }
        }
        if(right >= 0 && right <= nums.length-1){
            res[1] = nums[right] == target ? right : -1;
        }
        return res;
    }
}