（递归版） 归并排序

递归版的合并排序，时间复杂度为O(nlogn),空间复杂度为O(n+logn);

算法思想：

　　利用分而自治的思想，把排序分成两块，每块内部排序，再进行一次遍历排序即可，递归调用此过程即可。

主要代码：

void MergeSort(int *arr,int length){    Msort(arr,arr,0,length-1); }void Msort(int *arr1,int *arr2,int begin,int end){    int arr3[10];    int m;    if(begin == end)        arr2[begin] = arr1[end];    else{        m = (end + begin)/2;        Msort(arr1,arr3,begin,m);        Msort(arr1,arr3,m+1,end);        sort(arr3,arr2,begin,m,end);    }}void sort(int *arr3,int *arr1,int begin,int m,int end){    int i=begin,j=m+1,k,h;    for(k=i; i<=m && j<=end;k++){        if(arr3[i] < arr3[j])            arr1[k] = arr3[i++];        else            arr1[k] = arr3[j++];    }    if(i <= m){        for(h=0; h<=m-i;h++)            arr1[k+h] = arr3[i+h];    }else{        for(h=0; h<=end-j;h++)            arr1[k+h] = arr3[j+h];    }}

全部代码：

#include <stdio.h>#include <stdlib.h>#include <time.h>int arrtest1[10] = {3,4,7,8,0,9,1,2,6,5};int arrtest2[10] = {0,1,2,3,4,5,6,7,8,9};int arrtest3[10] = {9,8,7,6,5,4,3,2,1,0};void copy(int *from,int *arr,int length);void print(int *arr,int length);void MergeSort(int *arr,int length);void Msort(int *arr1,int *arr2,int begin,int end);void sort(int *arr3,int *arr1,int begin,int m,int end);int main(){    clock_t start,end;    int Arr[10];    int i;    copy(arrtest1,Arr,10);    print(Arr,10);    MergeSort(Arr,10);    print(Arr,10);    start = clock();    for(i=0;i<100000;i++){        copy(arrtest1,Arr,10);        //print(Arr,10);        MergeSort(Arr,10);        //print(Arr,10);    }    end = clock();    printf("first test:%d\n",end-start);    start = clock();    for(i=0;i<100000;i++){        copy(arrtest2,Arr,10);        //print(Arr,10);        MergeSort(Arr,10);        //print(Arr,10);    }    end = clock();    printf("first test:%d\n",end-start);    start = clock();    for(i=0;i<100000;i++){        copy(arrtest3,Arr,10);        //print(Arr,10);        MergeSort(Arr,10);        //print(Arr,10);    }    end = clock();    printf("first test:%d\n",end-start);        getchar();    return 0;}void MergeSort(int *arr,int length){    Msort(arr,arr,0,length-1); }void Msort(int *arr1,int *arr2,int begin,int end){    int arr3[10];    int m;    if(begin == end)        arr2[begin] = arr1[end];    else{        m = (end + begin)/2;        Msort(arr1,arr3,begin,m);        Msort(arr1,arr3,m+1,end);        sort(arr3,arr2,begin,m,end);    }}void sort(int *arr3,int *arr1,int begin,int m,int end){    int i=begin,j=m+1,k,h;    for(k=i; i<=m && j<=end;k++){        if(arr3[i] < arr3[j])            arr1[k] = arr3[i++];        else            arr1[k] = arr3[j++];    }    if(i <= m){        for(h=0; h<=m-i;h++)            arr1[k+h] = arr3[i+h];    }else{        for(h=0; h<=end-j;h++)            arr1[k+h] = arr3[j+h];    }}void copy(int *from,int *arr,int length){    int i;    for(i=0;i<length;i++){        arr[i] = from[i];    }}void print(int *arr,int length){    int i;    for(i=0;i<length;i++){        printf("%d ",arr[i]);    }    printf("\n");}

运行示例：