归并排序的递归和非递归实现

来源：互联网发布：邮箱注册淘宝的格式编辑：程序博客网时间：2024/05/22 08:16

归并排序是一个时间复杂度为O(nlogn)的算法，它可以由递归和非递归两种方式实现。

递归:

#include<iostream>using namespace std;void combine(int *nums,int l,int m,int r){   // cout<<"combine"<<l<<" "<<m<<" "<<r<<endl;   int len = r-l+1;    int *temp = new int[len+1];    int i = l;    int j = m+1;    int k =0;    while(i<=m && j <=r){        if(nums[i] >nums[j]){                temp[k++] = nums[j];                j++;        }else{            temp[k++] = nums[i];            i++;        }    }    while(i <=m) {temp[k++] = nums[i]; i++;}    while(j<=r) {temp[k++] = nums[j]; j++;}    k =0;    for(i =l;i<=r;i++) nums[i] = temp[k++];    delete []temp;}void merge_sort(int * nums,int left,int right){    if(left>=right) return;    int mid = (left+right)/2;    merge_sort(nums,left,mid);    merge_sort(nums,mid+1,right);    combine(nums,left,mid,right);}int main(){int nums[] = {5,4,2,1,6,8,9,3};int len = sizeof(nums)/sizeof(int);cout<<"before sort:";for(int i=0;i<len;i++) cout<<nums[i]<<" ";cout<<endl;merge_sort(nums,0,len-1);cout<<"after sort:";for(int i=0;i<len;i++) cout<<nums[i]<<" ";return 0;}

非递归实现:

#include<iostream>using namespace std;void combine(int *nums,int l,int m,int r){   // cout<<"combine"<<l<<" "<<m<<" "<<r<<endl;   int len = r-l+1;    int *temp = new int[len+1];    int i = l;    int j = m+1;    int k =0;    while(i<=m && j <=r){        if(nums[i] >nums[j]){                temp[k++] = nums[j];                j++;        }else{            temp[k++] = nums[i];            i++;        }    }    while(i <=m) {temp[k++] = nums[i]; i++;}    while(j<=r) {temp[k++] = nums[j]; j++;}    k =0;    for(i =l;i<=r;i++) nums[i] = temp[k++];    delete []temp;}void merge_sort(int * nums,int length){    for(int i = 1;i<length;i*=2){//枚举步长        int l = 0;        while(l<length-1){            int mid = l+i-1;            int r = mid +i;            if(mid>= length-1) break;//mid已经大于数组长度了，证明已经拍完            if(r>=length){  r = length -1;}//右边步长超过数组长度要退回到数组长            if(r ==mid) break;//只有左边，则排完了            combine(nums,l,mid,r);            l = r+1;        }    }}int main(){int nums[] = {5,4,2,1,6,8,9,3};int len = sizeof(nums)/sizeof(int);cout<<"before sort:";for(int i=0;i<len;i++) cout<<nums[i]<<" ";cout<<endl;merge_sort(nums,len);cout<<"after sort:";for(int i=0;i<len;i++) cout<<nums[i]<<" ";return 0;}

0 0