题解 | #Digital Roots#

#include<stdio.h>
#include<vector>
using namespace std;
int main(){
	int n;
	while (scanf("%d", &n) != EOF){
		while (n >= 10){
			vector<int>vec;
			int k;
			while (n != 0){
				k = n % 10;
				vec.push_back(k);
				n = n / 10;
			}
			for (int i = 0; i < vec.size(); i++){
				n = n + vec[i];
			}
		}
			printf("%d\n", n);
	}
}