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Leetcode Find Peak Element

时间:2015-10-23 01:31:18      阅读:162      评论:0      收藏:0      [点我收藏+]

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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.

click to show spoilers.

Note:

Your solution should be in logarithmic complexity.


解题思路:

一看complexity 要求,立即想到binary search.
如果中间元素大于其相邻后续元素,则中间元素左侧(包含该中间元素)必包含一个局部最大值。
如果中间元素小于其相邻后续元素,则中间元素右侧必包含一个局部最大值。

Java code:
public class Solution {
    public int findPeakElement(int[] nums) {
        int left = 0, 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;
    }
}

Reference:

1. http://blog.csdn.net/u010367506/article/details/41943309

2. https://leetcode.com/discuss/56031/java-short-and-neat-code-10-line

 

Leetcode Find Peak Element

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原文地址:http://www.cnblogs.com/anne-vista/p/4903291.html

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