自頂向下以及自底向上排序
具體原理不再介紹,參考《算法》,書上使用Java實現,此處寫一下C++版本,代碼如下:
//
// main.cpp
// algrithom
//
// Created by 嶽wenlong on 2017/6/4.
// Copyright © 2017年 嶽wenlong. All rights reserved.
//
#include <iostream>
#include <math.h>
using namespace std;
void merge(int* a,int lo,int mid,int hi) //歸併函數
{
int i = lo;
int j = mid+1;
int aux[hi+1];
for(int k=lo;k<=hi;k++)
{
aux[k] = a[k];
}
for(int k=lo;k<=hi;k++)
{
if(i>mid) a[k] = aux[j++]; //左半數組已經有序
else if(j>hi) a[k] = aux[i++]; //右半數組已經有序
else
{
if(aux[i]<aux[j]) a[k] = aux[i++];
else a[k] = aux[j++];
}
}
}
void sort_toptodown(int* a,int lo,int hi) //自頂向下排序
{
if(lo>=hi) return;
int mid = lo+(hi-lo)/2;
sort_toptodown(a,lo,mid); //遞歸調用自頂向下排序,排序左半數組
sort_toptodown(a,mid+1,hi); //遞歸調用自頂向下排序,排序右半數組
merge(a,lo,mid,hi);
}
void sort_toptodown(int* a,int length) //自頂向下排序
{
sort_toptodown(a,0,length-1);
}
void sort_downtotop(int* a,int length) //自底向上排序
{
for(int sz=1;sz<length;sz = sz*2) //歸併子數組大小爲sz,每次擴大一倍
{
for(int lo=0;lo<length-sz;lo = lo+2*sz) //子數組間進行歸併
{
merge(a,lo,lo+sz-1,(lo+2*sz-1<length-1)?(lo+2*sz-1):(length-1));
}
}
}
int main(int argc, const char * argv[]) {
int a[8] = {3,3,4,5,0,2,2,9};
int lenght = sizeof(a)/sizeof(a[0]);
sort_toptodown(a,lenght);
for(int i=0;i<8;i++)
{
cout<<a[i]<<" ";
}
cout<<endl;
return 0;
}