PAT (Advanced Level) Practice 1120 Friend Numbers （20 分）

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#include<cstdio>
#include<vector>
#include<map>
#include<cstring>
#include<algorithm>
using namespace std;

map<int, int> mp;
vector<int> ans;

int main()
{
	int n; scanf("%d", &n);
	for (int i = 1; i <= n; i++)
	{
		char s[10];
		scanf("%s", s);
		int len = strlen(s), sum = 0;
		for (int i = 0; i<len; i++)
			sum += s[i] - '0';
		mp[sum]++;
	}
	for (auto it : mp)
		if (it.second > 0)
			ans.push_back(it.first);
	ans.resize(unique(ans.begin(), ans.end()) - ans.begin());
	printf("%d\n", ans.size());
	for (int i = 0; i < ans.size(); i++)
		printf("%d%c", ans[i], " \n"[i + 1 == ans.size()]);
	return 0;
}