LeetCode-Java/FindPeakElement.java at master · phxcmos/LeetCode-Java

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Author: King, wangjingui@outlook.com

Date: Dec 06, 2014

Problem: Find Peak Element

Difficulty: Medium

Source: https://oj.leetcode.com/problems/find-peak-element/

Notes:

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.

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.

Find the peak element.

public class Solution {

public int findPeakElement(int[] num) {

int left = 0, right = num.length - 1, mid = -1;

while (left <= right) {

mid = (left + right) /2;

if ((mid == 0 || num[mid-1] <= num[mid]) && (mid == num.length - 1 || num[mid] >= num[mid+1]))

return mid;

if (mid > 0 && num[mid-1] > num[mid]) {

right = mid - 1;

} else if (num[mid+1] > num[mid]) {

left = mid + 1;

}

return mid;

}

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