LeetCode 852. Peak Index in a Mountain Array

LeetCode 852. Peak Index in a Mountain Array

Solution1：我的答案
时间复杂度 O(n) O ( n )

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

Solution2：
参考网址：https://leetcode.com/problems/peak-index-in-a-mountain-array/discuss/139891/c++-O(log-n)binary-serach
二分查找，时间复杂度 O(logn) O ( l o g n )

class Solution {
public:
    int peakIndexInMountainArray(vector<int>& A) {
        int l = 0,u= A.size()-1;
        int mid = (l+u)/2;
        while( !(A[mid]>A[mid-1] && A[mid]>A[mid+1]) ){
            if(A[mid]>A[mid-1]) l = mid+1;
            else u=mid-1;
            mid = (l+u)/2;
        }
        return mid;
    }
};

应该是要用二分查找做，否则也太无聊了