利用的不是数组而是向量，因为输入方便。
#include <iostream>
#include <vector>
#include <string>
#include<climits>
using namespace std;
void merge(vector<int> &a,int p,int q,int r){
int max=INT_MAX;
int n1=q-p+1;
int n2=r-q;
vector<int> L,R;
for(int i=0;i<n1;++i){
L.push_back(a[p+i]);}
for(int j=0;j<n2;++j){
R.push_back(a[q+j+1]);}
L.push_back(max);
R.push_back(max);
//for(auto i:L){cout<<i<<" ";}
//cout<<endl;
//for(auto i:R){cout<<i<<" ";}
//cout<<endl;
int i=0,j=0;
for(int k=p;k<=r;++k){
if(L[i]<=R[j]){
a[k]=L[i];
++i;}
else{
a[k]=R[j];
++j;}}}
void merge_sort(vector<int> &a,int p,int r){
if(p<r){
int q=(p+r)/2;
merge_sort(a,p,q);
merge_sort(a,q+1,r);
merge(a,p,q,r);}}
int main(){
vector<int> a;
int b;
while(cin>>b){a.push_back(b);}
for(auto i:a){cout<<i<<" ";}
cout<<endl;
int r=a.size();
merge_sort(a,0,r-1);
for(auto i:a){cout<<i<<" ";}
return 0;}
