uva 1310 - One-way traffic（连通分量）

题目链接：uva 1310 - One-way traffic

途中的桥不能变成单向边，其他的按照dfs顺序变成单向边。

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

using namespace std;
const int maxn = 2005;
const int maxm = 2 * 1e6 + 5;
typedef pair<int,int> pii;

struct State {
int a, b, c;
State(int a = 0, int b = 0, int c = 0): a(a), b(b), c(c) {}
};

int N, M, L[maxm], R[maxm], C[maxm];
int cntlock, pre[maxn], iscut[maxm];
vector<pii> G[maxn];
vector<State> ans;

int dfs (int u, int fa) {
int lowu = pre[u] = ++cntlock;

for (int i = 0; i < G[u].size(); i++) {
int v = G[u][i].first, e = G[u][i].second;
if (!pre[v]) {
int lowv = dfs(v, u);
lowu = min(lowu, lowv);
if (C[e] == 2) {
if (lowv > pre[u]) {
ans.push_back(State(u, v, 2));
iscut[e] = 1;
} else
ans.push_back(State(u, v, 1));
}
} else if (pre[v] < pre[u] && v != fa) {
lowu = min(lowu, pre[v]);
if (C[e] == 2)
ans.push_back(State(u, v, 1));
}
}
return lowu;
}

void findBCC() {
cntlock = 0;
memset(pre, 0, sizeof(pre));
memset(iscut, 0, sizeof(iscut));
for (int i = 1; i <= N; i++)
if (!pre[i]) dfs(i, -1);
}

void init () {
for (int i = 1; i <= N; i++) G[i].clear();

for (int i = 1; i <= M; i++) {
scanf("%d%d%d", &L[i], &R[i], &C[i]);
G[L[i]].push_back(make_pair(R[i], i));
if (C[i] == 2)
G[R[i]].push_back(make_pair(L[i], i));
}
ans.clear();
findBCC();
}

int main () {
while (scanf("%d%d", &N, &M) == 2) {
init();

for (int i = 0; i < ans.size(); i++)
printf("%d %d %d\n", ans[i].a, ans[i].b, ans[i].c);
}
return 0;
}