# Find-Peak-Element

Dec 08, 2017

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.

int findPeakElement(vector<int>& nums) {
return findPeakElement(nums,0,nums.size() - 1);
}
int findPeakElement1(vector<int> &nums,int first,int last) {
if (first > last) return -1;
int mid = (first + last)/2;
int a = 0;
if ( (mid+1 == nums.size() || nums[mid] > nums[mid + 1]) &&
(mid-1 < 0 || nums[mid] > nums[mid-1]) )
return mid;
int left = findPeakElement(nums,first,mid-1);
if (left != -1) return left;
return findPeakElement(nums,mid+1,last);
}


int findPeakElement(const vector<int> &num) {
return Helper(num, 0, num.size()-1);
}
int Helper(const vector<int> &num, int low, int high){
if(low == high)
return low;
else
{
int mid1 = (low+high)/2;
int mid2 = mid1+1;
if(num[mid1] > num[mid2])
return Helper(num, low, mid1);
else
return Helper(num, mid2, high);
}
}


int findPeakElement(const vector<int> &num)
{
int low = 0;
int high = num.size()-1;

while(low < high)
{
int mid1 = (low+high)/2;
int mid2 = mid1+1;
if(num[mid1] < num[mid2])
low = mid2;
else
high = mid1;
}
return low;
}

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