215题——Kth Largest Element in an Array（堆排序）

Kth Largest Element in an Array

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Question Solution

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.

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

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这道题目的意思是找出数组中的第K大的数，可以采用堆排序的方法，采用最大堆，每次找出未排序的数组中的最大值

这里需要注意的时堆调整函数

#include<iostream>
#include<vector>
using namespace std;
//这里的数组第0位存储的数字没有用
/*用来交换数组中两个元素的值*/
void swaped(vector<int>& nums,int i,int j)
{
int temp;
temp=nums[i];
nums[i]=nums[j];
nums[j]=temp;
}
//在数组nums中，除了第s外的从s+1...m满足最大堆顺序
void heapsort(vector<int>& nums,int s,int m)
{
int temp,j;
temp=nums[s];
for(j=2*s;j<=m;j=2*j)
{
if(j<m&&nums[j]<nums[j+1])
j++;
if(temp>nums[j])
break;
nums[s]=nums[j];
s=j;
}
nums[s]=temp;
}
//主函数
int findkthLargest(vector<int>& nums,int k)
{
vector<int> vec;
int n=nums.size();
vec.push_back(0);
for(int i=0;i<n;i++)
vec.push_back(nums[i]);

for(int i=n/2;i>=1;i--)
{
heapsort(vec,i,n);
}
int re;
for(int i=n;i>=1;i--)
{
swaped(vec,1,i);
k--;
re=vec[i];
if(k==0)
break;
heapsort(vec,1,i-1);
}
return re;

}
int main()
{
cout<<"hello yanliang"<<endl;
int ary[10]={7,6,5,4,3,2,1};
vector<int> vec(ary,ary+7);
cout<<findkthLargest(vec,4)<<endl;

/*
for(int i=1;i<=4;i++)
cout<<vec[i]<<' ';
cout<<endl;

heapsort(vec,2,4);
for(int i=1;i<=4;i++)
cout<<vec[i]<<' ';
cout<<endl;

heapsort(vec,1,4);
for(int i=1;i<=4;i++)
cout<<vec[i]<<' ';
cout<<endl;
*/

}