leetcode_Find Peak Element

描述：

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.

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Note:

Your solution should be in logarithmic complexity.

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

思路：

开始感觉很难下手，数组不是有序的，时间要求是log(n)，最后想到一种方法，mid=(left+right)/2;if(num[mid]<num[mid+1])left=mid+1;else right=mid,这种方式还真的可以找到其中的一个peak，所以根据时间复杂度的提示反而提醒了思路。

代码：

public int findPeakElement(int[] num) {
        int left=0,right=num.length-1;  
        int mid=0;
        int num1=0,num2=0;
        while(left<=right){  
            if(left==right)  
                return left;  
            mid=(left+right)/2; 
            if(num[mid]<num[mid+1])  
                left=mid+1;  
            else  
                right=mid;  
        } 
        return 0;
    }