[Leetcode 162] 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.

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solution1

public int findPeakElement(int[] nums) {
        int len = nums.length;
        if(len == 1) return 0;
        int max = nums[0];
        int index = 0;
        for(int i=1;i<len;i++){
            if(nums[i]>max){
                max = nums[i];
                index = i;
            }
        }
        return index;
    }

solution2

public class Solution {
    public int findPeakElement(int[] nums) {
        if(nums.length == 1) return 0;
        for(int i=1;i<nums.length;i++){
            if(nums[i]<nums[i-1]){
                return i-1;
            }
        }
        return nums.length-1;
    }
}

solution3

public int findPeakElement(int[] nums) {
        if(nums.length ==1) return 0;
        int low = 0;
        int high = nums.length-1;
        while(low < high){
            int mid = (low + high)/2;
            if(nums[mid]<nums[mid+1]) 
                low = mid+1;
            else
                high = mid;
        }
        return low;
    }