zoukankan      html  css  js  c++  java
  • Find Peak Element 解答

    Question

    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.

    Note:

    Your solution should be in logarithmic complexity.

    Solution

    The assumption is a very good hint. It assures that there must be a peak in input array.

    We can solve this problem by Binary Search.

    Four situations to consider:

    1. nums[mid] > nums[mid - 1] && nums[mid] > nums[mid + 1]

    => mid is a peak

    2. nums[mid] > nums[mid - 1] && nums[mid] < nums[mid + 1]

    => There must exists a peak in right side

    3. nums[mid] < nums[mid - 1] && nums[mid] > nums[mid + 1]

    => There must exists a peak in left side

    4. nums[mid] < nums[mid - 1] && nums[mid] < nums[mid + 1]

    => Either in right or left side, there must exists a peak.

     1 public class Solution {
     2     public int findPeakElement(int[] nums) {
     3         // Binary Search to find peak
     4         int start = 0, end = nums.length - 1, mid = 0, prev = 0, next = 0;
     5         while (start + 1 < end)  {
     6             mid = (end - start) / 2 + start;
     7             prev = mid - 1;
     8             next = mid + 1;
     9             if (nums[mid] > nums[prev] && nums[mid] > nums[next])
    10                 return mid;
    11             if (nums[mid] > nums[prev] && nums[mid] < nums[next]) {
    12                 start = mid;
    13                 continue;
    14             }
    15             if (nums[mid] < nums[prev] && nums[mid] > nums[next]) {
    16                 end = mid;
    17                 continue;
    18             }
    19             start = mid;
    20         }
    21         if (nums[start] > nums[end])
    22             return start;
    23         return end;
    24     }
    25 }
  • 相关阅读:
    04: vue生命周期和实例属性和方法
    03: vuejs 事件、模板、过滤器
    (打补丁 )patch
    zabbix安装
    zabbix简介
    linux 虚拟网络模型介绍
    虚拟化
    虚拟化分类(半虚拟化和全虚拟化)
    playbook详解—YAML格式的文本
    ansible的介绍和一些基本模块介绍
  • 原文地址:https://www.cnblogs.com/ireneyanglan/p/4889395.html
Copyright © 2011-2022 走看看