Leetcode - Array - 162. Find Peak Element（水题）

1. Problem Description

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.

输出数组中任意一个大于其左邻右邻的数字的下标。

 

2. My solution

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

利用这句话很容易写出：

int findPeakElement(vector<int>& nums) {
         int len=nums.size();
         const int INF=1<<32-1;
         nums.push_back(-INF);
         int ansidx=0;
         for(int i=1;i<len;i++)
            if(nums[i]>nums[i-1]&&nums[i]>nums[i+1])
               ansidx=i;
         return ansidx;
    }