自顶向下的归并排序

归并排序

自顶向下的归并排序

Notes:

1. 也就比合并有序链表多了拆分的步骤
2. 写完后可以优化下代码行数

/*
自顶向下的归并排序
*/
#include <iostream>
using namespace std;

void Merge(int* arr1,int len1,int* arr2,int len2){
	int* tmp = new int[len1+len2];
	int i = 0,j = 0,k = 0;
	while( i != len1 && j != len2){
		if(arr1[i] <= arr2[j]){
			tmp[k++] = arr1[i++];
		}
		else{
			tmp[k++] = arr2[j++];
		}
	}
	while(j < len2){
		tmp[k++] = arr2[j++];
	}
	while(i < len1){
		tmp[k++] = arr1[i++];
	}
	for(i = 0;i < k;i++){
		arr1[i] = tmp[i];
	}
	delete []tmp;
	tmp = NULL;
}
void MergeSort(int* arr,int len){
	if(len > 1){
		int* arr1 = arr;
		int arr1_len = len/2;
		int* arr2 = arr + arr1_len;
		int arr2_len = len - arr1_len;
		//分解
		MergeSort(arr1,arr1_len);
		MergeSort(arr2,arr2_len);
		//合并
		Merge(arr1,arr1_len,arr2,arr2_len);
	} 
}

void Print(int* arr,int len){
	for(int i = 0;i < len;i++){
		cout<<arr[i]<<"  ";
	}
	cout<<endl;
}
int main(int argc, char const *argv[])
{
	int arr[8] = {2,4,11,0,1,9,6,7};
	Print(arr,8);
	MergeSort(arr,8);
	Print(arr,8);
	
	return 0;
}

用下标的归并排序算法

#include <iostream>
#include <cstring>
using namespace std;

void Print_(int* arr,int len){
	for(int i = 0;i < len;i++){
		cout<<arr[i]<<"  ";
	}
	cout<<"tmp "<<endl;
}
void Merge(int* arr,int l,int m,int r){
	int tmp_size = r-l+1;
	int* tmp =new int[tmp_size];
	//memcpy(tmp,arr,tmp_size*sizeof(int));
	for(int i = l;i <=r;i++){
		tmp[i-l] = arr[i];
	}
	int i = l,j = m+1;
	for(int k = l;k <= r;k++){	//为啥要写=
		if(i > m){		//左边循环完
			arr[k] = tmp[j-l];
			j++;
		}
		else if(j > r){		//右边循环完
			arr[k] = tmp[i-l];
			i++;
		}
		else if(tmp[i-l] <= tmp[j-l]){
			arr[k] = tmp[i-l];
			i++;
		}
		else{
			arr[k] = tmp[j-l];
			j++;
		}
	}
	//Print_(arr,tmp_size);
	delete []tmp;
	tmp = NULL;
}
void MergeSort(int* arr,int l,int r){
	cout<<"deal with ["<<l<<"---"<<r<<"]"<<endl;
	if(l >= r){
		return ;
	}
	else{
		int m = (r+l)/2;		//(r+l)/2
		MergeSort(arr,l,m);
		MergeSort(arr,m+1,r);
		Merge(arr,l,m,r);
	}
}
void Print(int* arr,int len){
	for(int i = 0;i < len;i++){
		cout<<arr[i]<<"  ";
	}
	cout<<endl;
}
int main(int argc, char const *argv[])
{
	int arr[7] = {55,4,53,2,8,7,0};
	Print(arr,7);
	MergeSort(arr,0,6);
	Print(arr,7);
	return 0;
}

本来想更新到码云上,为啥抽风了。。。。

参考链接：

1. C++实现自顶向下的归并排序算法
2. 玩转算法