[LeetCode] 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
= -∞

.

For example, in array

[1, 2, 3, 1]

, 3 is a peak element and your function should return the index number 2.

click to show spoilers.

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

Hide Tags

Array Binary Search

分析：
参考 http://www.cnblogs.com/diegodu/p/4589781.html 这个是找局部最小

此题是找局部最大

class Solution {
public:
int findPeakElement(vector<int>& nums)
{
if(nums.size() == 0)
return -1;
if(nums.size() == 1)
return 0;
if(nums[0] > nums[1])
return 0;

int size = nums.size();
if(nums[size - 1] > nums[size - 2])
return size - 1;

int low = 1;
int high = size - 2;
int mid;

while(low < high)
{
mid = (low + high)/2;
if(nums[mid] < nums[mid+1])
{
low = mid+1;
}
else if(nums[mid] < nums[mid-1])
{
high = mid-1;
}
else
return mid;
}
return low;

}
};