HDU 4738 Caocao's Bridges（找割边）

HDU 4738 Caocao's Bridges

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

const int N = 1005;
const int INF = 0x3f3f3f3f;

int pre
, low
, dfs_clock;

int n, m;

struct Node {
int v, val, id;
Node() {}
Node(int v, int val, int id) {
this->v = v;
this->val = val;
this->id = id;
}
};

vector<Node> g
;
int ans;

int dfs(int u, int fa) {
int lowu = pre[u] = ++dfs_clock;
for (int i = 0; i < g[u].size(); i++) {
int v = g[u][i].v;
int id = g[u][i].id;
if (id == fa) continue;
if (!pre[v]) {
int lowv = dfs(v, id);
lowu = min(lowu, lowv);
if (lowv > pre[u])
ans = min(ans, g[u][i].val);
} else lowu = min(lowu, pre[v]);
}
return low[u] = lowu;
}

int main() {
while (~scanf("%d%d", &n, &m) && n) {
int u, v, val;
memset(pre, 0, sizeof(pre));
dfs_clock = 0;
for (int i = 0; i < n; i++)
g[i].clear();
for (int i = 0; i < m; i++) {
scanf("%d%d%d", &u, &v, &val);
u--; v--;
g[u].push_back(Node(v, val, i));
g[v].push_back(Node(u, val, i));
}
int cnt = 0;
ans = INF;
for (int i = 0; i < n; i++) {
if (!pre[i]) {
cnt++;
dfs(i, -1);
}
}
if (cnt > 1) printf("0\n");
else if (ans == INF) printf("-1\n");
else {
if (ans == 0) ans = 1;
printf("%d\n", ans);
}
}
return 0;
}