堆排序

堆类似一颗完全二叉树，根节点是一个最值，同时它的左右两颗子树也是堆。下面以最大堆为例，插入操作跟插入排序是一样的，把新加入的节点放到树的最后面，然后跟它的父亲比较，如果比父亲比它小，则互换位置，直到找到某个祖先节点大于它时停止。取最大值则直接取根节点，若删去该节点，则要重新调整堆，使得该堆仍是最大堆。做法是把树中最后一个节点放到根节点，然后向下查找，跟其值最小的孩子互换位置，直到找到一个大于它的子孙节点便终止。

 

#include <iostream>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <cstdlib>

using namespace std;

void update_down(int *heap,int pos,int sum)
{
    int tem = heap[pos];
    int son = pos<<1;
    while(son <= sum)
    {
        if(son < sum && heap[son] < heap[son+1])
            son++;
        if(heap[son] > tem)
        {
            heap[pos] = heap[son];
            pos = son, son = pos<<1;
        }
        else
            break;
    }
    heap[pos] = tem;
}

void update_up(int *heap,int pos,int sum)
{
    int tem = heap[pos];
    int father = pos>>1;
    while(father > 0 && heap[father] < tem)
    {
        heap[pos] = heap[father];
        pos = father, father = pos>>1;
    }
    heap[pos] = tem;
}

int main()
{
    int len, *heap;
    cin >> len;
    heap = new int [len+1];
    srand((int)time(0));
    int startTime = clock();
    for(int i=1; i<=len; i++)
    {
        heap[i] = rand()%512 + 1;
        update_up(heap,i,i);
    }
    int sum = len;
    while(sum)
    {
       // cout << heap[1] << " ";
        heap[1] = heap[sum--];
        update_down(heap,1,sum);
    }
    int endTime = clock();
    cout << "\nused time: " << endTime - startTime << endl;
}