uva 11080 - Place the Guards（二分图染色）

题目链接：uva 11080 - Place the Guards

#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>

using namespace std;
const int maxn = 205;

int N, M, B, W, C[maxn];
vector<int> G[maxn];

void init () {
scanf("%d%d", &N, &M);
memset(C, 0, sizeof(C));
for (int i = 0; i < N; i++) G[i].clear();

int u, v;
while (M--) {
scanf("%d%d", &u, &v);
G[u].push_back(v);
G[v].push_back(u);
}
}

bool bipartite(int u) {
if (C[u] == 1) B++;
else W++;
for (int i = 0; i < G[u].size(); i++) {
int v = G[u][i];
if (C[v] == C[u]) return false;
if (!C[v]) {
C[v] = 3 - C[u];
if (!bipartite(v)) return false;
}
}
return true;
}

int solve () {
int ans = 0;
for (int i = 0; i < N; i++) {
if (C[i] == 0) {
B = W = 0;
C[i] = 1;
if (!bipartite(i)) return -1;
ans += max(1, min(B, W));
}
}
return ans;
}

int main () {
int cas;
scanf("%d", &cas);
while (cas--) {
init();
printf("%d\n", solve());
}
return 0;
}