Submission #2514052

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Source Code Expand

#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <stack>

#define REP(i,n) for(int i = 0; i < (n); i++)
#define REPC(x,c) for(auto x:(c))
#define FOR(i, b, e) for(int i = (b); i < (e); i++)
#define VS vector<string>
#define VI vector<int>
#define VVI vector<vector<int>>

using namespace std;

int main() {
	int n, m;
	cin >> n >> m;
	VVI edges;
	REP(i, m) {
		int x, y;
		cin >> x >> y;
		edges.push_back({ x,y });
	}

	set<int> allMemo;
	int count = 0;
	FOR(node, 1, n+1) {
		if (allMemo.find(node) != allMemo.end()) {
			continue;
		}
		bool flg = true;

		stack<int> stk;
		set<int> memo = {node};
		allMemo.insert(node);
		stk.push(node);

		while (!stk.empty()) {
			int nextNode = stk.top();
			stk.pop();
			int c = 0;
			REPC(edge, edges) {
				REP(i, 2) {
						if (edge[i] == nextNode) {
						int to = edge[1 - i];
						if (memo.find(to) == memo.end()) {
							stk.push(to);
							memo.insert(to);
							allMemo.insert(to);
						} else {
							c++;
						}
					}
				}
			}
			if (c >= 2) { flg = false; }
		}

		if (flg) {
			count++;
		}
	}
	cout << count << endl;
}

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