【数组】Find Peak Element

题目：

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.

思路：

按照题意，num[0]是大于左边的不存在的那个元素的，num[size-1]也是大于右边那个不存在的元素的，假如不存在，那么就会有num[0]<num[1]，num[1]<num[2]，就是增序，num[size-2]<num[size-1]，这样num[size-1]就是peak elem了，所以一定存在。于是就是这样的思路，num[NULL] < num[0],我们假设左边的元素小于右边的元素，那么第一个左边元素大于右边的那个一定是peak elem.如num[0]。

/**
 * @param {number[]} nums
 * @return {number}
 */
var findPeakElement = function(nums) {
    var n=nums.length;
    for(var i=1;i<n;i++){
        if(nums[i]<nums[i-1]){
            return i-1;
        }
    }
    
    return n-1;
};