二分查找向左或向右紧缩

 class Solution {
     public int[] searchRange(int[] nums, int target) {
   int[] res=new int[2];
      
                  res[0]=findleft(nums,target);
                  res[1]=findright(nums,target);
                  return res;
     }

     private int findright(int[] nums, int target) {
      int left=0;
      int right=nums.length;   //向左或向右紧缩时，就用nums.length; 因此while里为<号 不带等号 等就越界
      while (left<right) {
     int mid=(left+right)>>1;
      if (nums[mid]==target) {
       left=mid+1;    //向右，因为是right=nums.length;所以是左闭右开
      }
      else if (nums[mid]<target) {
       left=mid+1;
      }
      else {
       right=mid;
      }
    }
     if (left == 0) return -1;    //向右紧缩  却缩到了最左侧 说明没找到
                return nums[left-1] == target ? (left-1) : -1;
   }

   private int findleft(int[] nums, int target) {
     int left=0;
      int right=nums.length;
      while (left<right) {
     int mid=(left+right)>>1;
      if (nums[mid]==target) {
       right=mid;      //向左紧缩，因为是right=nums.length;所以是左闭右开
      }
      else if (nums[mid]<target) {
       left=mid+1;
      }
      else {
       right=mid;
      }
    }
   if (left >= nums.length || nums[left] != target)//向左紧缩，却缩到了最右侧 说明没找到
                      return -1;
           return left;

   }
 }