class Solution {
public:
    int missingNumber(vector<int>& nums) {
        //二分查找
        int left=0,right=nums.size()-1;
        while(left<=right){
            int mid=left+((right-left)>>1);
            if(nums[mid]==mid){     //想清楚需要查找的数字在哪一块区域
                left=mid+1;
            }
            else{
                right=mid-1;
            }
        }
        return left;
    }
};