Find Peak Element

A peak element is an element that is greater than its neighbors.

Given an input array where num[i] ≠ num[i+1], find a peak element and return its index.

The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.

You may imagine that num[-1] = num[n] = -∞.

For example, in array [1, 2, 3, 1], 3 is a peak element and your function should return the index number 2.

解法如下，这个复杂度是不是O(lgn)呢？需要再看看

class Solution {
public:
    int findPeakElement(const vector<int> &num) {
        int n = num.size();
        if(n==1||num[0]>num[1]) return 0;
        if(num[n-1]>num[n-2]) return n-1;
        for(int i=1; i<=n-2;){
            if(num[i]<num[i-1]) i=+2;
            else if(num[i]>num[i+1]) return i;
            else i++;
        }
    }
};