算法1

暴力枚举

18ms

class Solution {
public:
    int getNumberSameAsIndex(vector<int>& nums) {
        for (int i = 0; i < nums.size(); i ++ )
            if (nums[i] == i) return i;
        return -1;
    }
};

算法2

二分查找

22ms

class Solution {
public:
    int getNumberSameAsIndex(vector<int>& nums) {
        int l = 0, r = nums.size() - 1;
        while(l<r)
        {
            int mid = l + r >> 1;
            if (nums[mid] >= mid) r = mid;
            else l = mid + 1;
        }
        if(nums[r] == r) return r;
        else return -1;
    }
};