Question

Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.

For example,
Given [3,2,1,5,6,4] and k = 2, return 5.

Note: 
You may assume k is always valid, 1 ≤ k ≤ array's length.

Solution 1 -- PriorityQueue

1. 将所有元素放入heap中

2. 依次用poll()取出heap中最大值

 public class Solution {
public int findKthLargest(int[] nums, int k) {
if (nums == null || k > nums.length)
return 0;
int length = nums.length, index = length - k, result = 0;
PriorityQueue<Integer> pq = new PriorityQueue<Integer>(length,
new Comparator<Integer>(){
public int compare(Integer a, Integer b) {
return (a - b);
}
});
for (int i = 0; i < length; i++)
pq.add(nums[i]);
while (index >= 0) {
result = pq.poll();
index--;
}
return result;
}
}

Improvement

 public class Solution {
public int findKthLargest(int[] nums, int k) {
if (nums == null || k > nums.length)
return 0;
int length = nums.length, index = k, result = 0;
PriorityQueue<Integer> pq = new PriorityQueue<Integer>(length, Collections.reverseOrder());
for (int i = 0; i < length; i++)
pq.add(nums[i]);
while (index > 0) {
result = pq.poll();
index--;
}
return result;
}
}

Solution 2 -- Quick Select

Quick Sort in Java

Average Time O(n)

 '''
a: [3, 2, 5, 1], 2
output: 2
''' def swap(a, index1, index2):
if index1 >= index2:
return
tmp = a[index1]
a[index1] = a[index2]
a[index2] = tmp def partition(a, start, end):
''' a[start:end]
pivot: a[end]
return: index of pivot
'''
pivot = a[end]
cur_big = start - 1
for i in range(start, end):
if a[i] >= pivot:
cur_big += 1
swap(a, cur_big, i)
cur_big += 1
swap(a, cur_big, end)
return cur_big def quick_select(a, k):
k -= 1
length = len(a)
start = 0
end = length - 1
while start < end:
index = partition(a, start, end)
if index == k:
return a[index]
if index > k:
# Note: end != index
end = index - 1
else:
# Note: start != index
start = index + 1
k = k - index
return -1 a = [3, 2, 5, 1]
k = 1
print(quick_select(a, k))

Kth Largest Element in an Array 解答的更多相关文章

  1. Kth Largest Element in an Array

    Find K-th largest element in an array. Notice You can swap elements in the array Example In array [9 ...

  2. leetcode面试准备:Kth Largest Element in an Array

    leetcode面试准备:Kth Largest Element in an Array 1 题目 Find the kth largest element in an unsorted array. ...

  3. 【LeetCode】215. Kth Largest Element in an Array (2 solutions)

    Kth Largest Element in an Array Find the kth largest element in an unsorted array. Note that it is t ...

  4. 剑指offer 最小的k个数 、 leetcode 215. Kth Largest Element in an Array 、295. Find Median from Data Stream(剑指 数据流中位数)

    注意multiset的一个bug: multiset带一个参数的erase函数原型有两种.一是传递一个元素值,如上面例子代码中,这时候删除的是集合中所有值等于输入值的元素,并且返回删除的元素个数:另外 ...

  5. Leetcode 之 Kth Largest Element in an Array

    636.Kth Largest Element in an Array 1.Problem Find the kth largest element in an unsorted array. Not ...

  6. [Leetcode Week11]Kth Largest Element in an Array

    Kth Largest Element in an Array 题解 题目来源:https://leetcode.com/problems/kth-largest-element-in-an-arra ...

  7. Lettcode Kth Largest Element in an Array

    Lettcode Kth Largest Element in an Array 题意:在无序数组中,寻找第k大的数字,注意这里考虑是重复的. 一直只会简单的O(nlogn)的做法,听说这题有O(n) ...

  8. 网易2016 实习研发工程师 [编程题]寻找第K大 and leetcode 215. Kth Largest Element in an Array

    传送门 有一个整数数组,请你根据快速排序的思路,找出数组中第K大的数. 给定一个整数数组a,同时给定它的大小n和要找的K(K在1到n之间),请返回第K大的数,保证答案存在. 测试样例: [1,3,5, ...

  9. LN : leetcode 215 Kth Largest Element in an Array

    lc 215 Kth Largest Element in an Array 215 Kth Largest Element in an Array Find the kth largest elem ...

随机推荐

  1. DBA 经典面试题(4)

    1.如果信息采集管理系统(ICM)崩溃了怎么办?  答案:所有其他的管理器都会继续工作.ICM只会处理队列控制请求,意思是开启和关闭其他并发的管理器.    2.你如何加速打补丁的过程?    答案: ...

  2. C#开发客户端、JAVA和tomcat开发服务端

    hessian入门,Hello和文件上传范例,C#客户端+Java Tomcat后台 2.Hello范例1)后台--定义Java接口:package org.migle.hessian; public ...

  3. 一段代码说明javascript闭包执行机制

    假设你能理解以下代码的执行结果,应该就算理解闭包的执行机制了. var name = "tom"; var myobj = { name: "jackson", ...

  4. 打印log 保存log

    using UnityEngine; using System.Collections; using System.IO; using System; using System.Text; names ...

  5. C++空类中的默认函数

    定义一个空的C++类,例如 class Empty { } 一个空的class在C++编译器处理过后就不再为空,编译器会自动地为我们声明一些member function,一般编译过去就相当于 cla ...

  6. Android应用程序资源的编译和打包过程分析

    文章转载至CSDN社区罗升阳的安卓之旅,原文地址:http://blog.csdn.net/luoshengyang/article/details/8744683 我们知道,在一个APK文件中,除了 ...

  7. [HeadFirst-HTMLCSS学习笔记][第十二章HTML5标记]

    考虑HTML结构 HTML5即是把原来<div>换成一些更特定的元素.能够更明确指示包含什么内容. (页眉,导航,页脚,文章) article nav 导航 header footer t ...

  8. 禁止 favicon.ico 请求

    favicon.ico 图标用于收藏夹图标和浏览器标签上的显示,如果不设置,浏览器会请求网站根目录的这个图标,如果网站根目录也没有这图标会产生 404.出于优化的考虑,要么就有这个图标,要么就禁止产生 ...

  9. VML :Vector Markup Language

    在以前老是浏览器IE<9在不支持SVG情况下,IE一般通过VML来绘制图形,图片,文字等 步骤: 必须在头部添加 <HTML xmlns:v="urn:schemas-micro ...

  10. 关于android的SQLiteDatabase和Cursor的一些疑问

    android数据库操作的基础有三个类:SQLiteOpenHelper,SQLiteDatabase和Cursor.其中,SQLiteOpenHelper会建立一个数据库连接,它虽然可以调用多次ge ...