C++14(g++5.4) 解法, 执行用时: 6ms, 内存消耗: 608K, 提交时间: 2019-05-01 13:04:19

#include<bits/stdc++.h>

using namespace std;
int a[13]={1,4,5,9,10,40,50,90,100,400,500,900,1000};
string b[13]={"I","IV","V","IX","X","XL","L","XC","C","CD","D","CM","M"};
int main()
{
	int n;
	cin>>n;
	while(n)
	{
		int i;
		for(i=12;i>=0;i--)
		{
			if(n/a[i])
				break;
		}
		for(int j=0;j<n/a[i];j++)
			cout<<b[i];
		n=n%a[i];
	}
	cout<<endl;
	return 0; 
} 

C++11(clang++ 3.9) 解法, 执行用时: 5ms, 内存消耗: 504K, 提交时间: 2019-04-22 19:31:10

#include<stdio.h>
#include<bits/stdc++.h>
using namespace std;
string S[]={"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};
int num[]={1000,900,500,400,100,90,50,40,10,9,5,4,1};
int main(){
	int n;cin>>n;
	for(int i=0;i<=12;i++){
		if(n>=num[i]){
			n-=num[i];
			cout<<S[i];
			i--;
		}
	}
	return 0;
}

Python3(3.5.2) 解法, 执行用时: 32ms, 内存消耗: 3576K, 提交时间: 2019-04-20 14:32:02

a = [1000,900,500,400,100,90,50,40,10,9,5,4,1]
b = ['M','CM','D','CD','C','XC','L','XL','X','IX','V','IV','I']
c = [0 for i in range(13)]
n = int(input())
for i in range(13):
    c[i] = b[i] * (n // a[i])
    n %= a[i]
for i in c:
    print(i,end="")
print()