'commit'

TangDou/AcWing/DCC/T103489.cpp

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+#include <bits/stdc++.h>
+
+using namespace std;
+//此题是P8436的弱化版本，弱化了记录每个边双中点有哪些:vector<int> belong[N];
+const int N = 500010, M = 2000010 * 2;
+
+int n, m;
+
+int dfn[N], low[N], ts, stk[N], top;
+vector<int> belong[N]; //边双中有哪些原始点
+
+int id[N], dcc_cnt; //原始点x属于哪个边双连通分量，dcc_cnt指边双连通分量个数
+int is_bridge[M];   //记录哪些边是割边
+
+//链式前向星
+int e[M], h[N], idx, w[M], ne[M];
+void add(int a, int b, int c = 0) {
+    e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx++;
+}
+
+//边双连通分量
+void tarjan(int u, int fa) {
+    dfn[u] = low[u] = ++ts;
+    stk[++top] = u;
+    for (int i = h[u]; ~i; i = ne[i]) {
+        int j = e[i];
+        if (!dfn[j]) {
+            tarjan(j, i);
+            low[u] = min(low[u], low[j]);
+            if (dfn[u] < low[j]) is_bridge[i] = is_bridge[i ^ 1] = true; //记录割边
+        } else if (i != (fa ^ 1))
+            low[u] = min(low[u], dfn[j]);
+    }
+
+    if (dfn[u] == low[u]) {
+        ++dcc_cnt; //边双数量+1
+        int x;
+        do {
+            x = stk[top--];
+            id[x] = dcc_cnt;              // 记录点与边双关系
+            belong[dcc_cnt].push_back(x); // 记录边双中有哪些点
+        } while (x != u);
+    }
+}
+
+int main() {
+    scanf("%d %d", &n, &m);
+    memset(h, -1, sizeof h);
+
+    for (int i = 0; i < m; i++) {
+        int a, b;
+        scanf("%d %d", &a, &b);
+        add(a, b), add(b, a);
+    }
+
+    for (int i = 1; i <= n; i++)
+        if (!dfn[i]) tarjan(i, -1);
+
+    //输出边双个数
+    printf("%d\n", dcc_cnt);
+
+    // for (int i = 1; i <= dcc_cnt; i++) {
+    //     //此边双中点的数量
+    //     printf("%d ", belong[i].size());
+    //     //此边双中都有哪些点
+    //     for (int j = 0; j < belong[i].size(); j++)
+    //         printf("%d ", belong[i][j]);
+    //     puts("");
+    // }
+
+    return 0;
+}