Find Peak Element

最新推荐文章于 2024-11-13 02:34:54 发布

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最新推荐文章于 2024-11-13 02:34:54 发布

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原文链接：http://www.cnblogs.com/beiyeqingteng/p/10993033.html

本文介绍了一种寻找峰值元素的算法，峰值元素是指大于其邻居的元素。提供了两种解决方案，一种是一般解法，另一种是更高效的O(lgN)解法，通过二分查找来快速定位峰值元素。

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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.

分析：一般解法：

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

O(lgN)解法　　

 1 public class Solution {
 2     public int findPeakElement(int[] nums) {
 3         int l = 0, r = nums.length - 1;
 4         while (l < r) {
 5             int mid = (l + r) / 2;
 6             if (nums[mid] > nums[mid + 1]) // as l < r
 7                 r = mid;
 8             else
 9                 l = mid + 1;
10         }
11         return l;
12     }
13 }