leetcode 34.在排序数组中查找元素的第一个和最后一个位置（Java 二分查找 medium 重要）

https://leetcode-cn.com/problems/find-first-and-last-position-of-element-in-sorted-array/

二分查找详解：

https://leetcode-cn.com/problems/find-first-and-last-position-of-element-in-sorted-array/solution/er-fen-cha-zhao-suan-fa-xi-jie-xiang-jie-by-labula/

 

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