【每日一题】打卡 68

原题链接：Problem - E - Codeforces

思路 ：根据题意得出若该图存在奇环或者一个数出现三次则无解，反之有解，利用染色法+map判断即可。

void add(int a, int b) {
	e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}
bool dfs(int u, int c) {
	col[u] = c;
	for (int i = h[u]; ~i; i = ne[i]) {
		int j = e[i];
		if (!col[j]) {
			if (!dfs(j, !c)) return false;
		} else if (col[j] == c)
			return false;
	}
	return true;
}
void solve() {
	map<int, int> mp;
	int f = 0;
	idx = 0;
	mem(col, 0);
	mem(h, -1);
	cin >> n;
	for (int i = 1; i <= n; i++) {
		int a, b;
		cin >> a >> b;
		if (mp[a] == 2 || mp[b] == 2) f = 1;
		mp[a]++, mp[b]++;
		add(a, b);
		add(b, a);
	}
	if (f) {
		no;
		return;
	}
	for (int i = 1; i <= n; i++) {
		if (!col[i])
			if (!dfs(i, 0)) {
				no;
				return;
			}
	}
	yes;
}