[Leetcode + Lintcode] 162. Find Peak Element

Posted 2020-08-19

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.

 

1. Java

public class Solution {
    public int findPeakElement(int[] nums) {
        if(nums == null ||nums.length == 0){
            return 0;
        }
        int left = 0;
        int right = nums.length - 1;
        while(left < right){
            int mid = left + (right-left)/2;
            if(nums[mid] < nums[mid+1]){
                left = mid+1;
            }
            else{
                right = mid;
            }
        }
        return left;
    }
}

 

2. Python

class Solution:
    #@param A: An integers list.
    #@return: return any of peek positions.
    def findPeak(self, A):
        # write your code here
        if A is None or len(A) == 0:
            return 0
        left = 0
        right = len(A) - 1
        while(left < right):
            mid = left + (right-left)/2
            if A[mid] < A[mid+1]:
                left = mid + 1
            else:
                right = mid
        return left