二分图 最大匹配 60pts求调

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pll;
const int N = 1e4 + 10, M = 2e5 + 10;
int n, m, ans;
int h[N], e[M], ne[M], idx;
int match[N], color[N];
bool st[N];
void add(int a, int b) {
	e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}
bool dfs(int u, int c) {
	color[u] = c;
	for (int i = h[u] ; ~i ; i = ne[i]) {
		int j = e[i];
		if (!color[j]) {
			if (!dfs(j, 3 - c)) return false;
		} else {
			if (color[j] == c) return false;
		}
	}
	return true;
}
bool find(int u) {
	for (int i = h[u]; ~i; i = ne[i]) {
		int j = e[i];
		if(!st[j])
		{
			st[j] = 1;
			if (!match[j] || find(match[j])) {
				match[j] = u;
				return true;
			}			
		}
	}
	return false;
}
int main() {
	cin >> n >> m;
	memset(h, -1, sizeof h);
	while (m--) {
		int a, b;
		cin >> a >> b;
		add(a, b), add(b, a);
	}
	bool f = 1;
	for (int i = 1 ; i <= n ; ++i) {
		if (!color[i]) {
			if (!dfs(i, 1)) {
				f = 0;
				break;
			}
		}
	}
	if (!f) 
	{
		puts("Impossible");
		return 0;
	}
	else {
		for (int i = 1 ; i <= n; ++i) {
			if (color[i] == 1) {
				memset(st, 0, sizeof st);
				if (find(i)) ans++;
			}
		}
	}
	cout << ans << endl;
	return 0;
}