Tarjan算法求无向图的割边和割点

#include <bits/stdc++.h>

using namespace std;
const int SIZE = 1e5 + 10;
int head[SIZE], ver[SIZE * 2], Next[SIZE * 2];
int dfn[SIZE], low[SIZE], n, m, tot, num;
bool bridge[SIZE * 2];

void add(int x, int y) {
    ver[++tot] = y;
    Next[tot] = head[x];
    head[x] = tot;
}

void tarjan(int x, int in_edge) {
    dfn[x] = low[x] = ++num;
    for (int i = head[x]; i; i = Next[i]) {
        int y = ver[i];
        if (!dfn[y]) {
            tarjan(y, i);
            low[x] = min(low[x], low[y]);
            if (low[y] > dfn[x])
                bridge[i] = bridge[i ^ 1] = true;
        } else if (i != (in_edge ^ 1))
            low[x] = min(low[x], dfn[y]);
    }
}

int main() {
    cin >> n >> m;
    tot = 1;
    for (int i = 1; i <= m; i++) {
        int x, y;
        scanf("%d%d", &x, &y);
        add(x, y);
        add(y, x);
    }
    for (int i = 1; i <= n; i++)
        if (!dfn[i])
            tarjan(i, 0);
    for (int i = 2; i < tot; i += 2)
        if (bridge[i])
            printf("%d %d\n", ver[i ^ 1], ver[i]);
    return 0;
}

input:
9 11
1 2
2 3
3 4
4 5
5 1
5 2
1 6
6 9
6 8
9 8
6 7
output:
1 6
6 7

#include <bits/stdc++.h>

using namespace std;
const int SIZE = 1e5 + 10;
int head[SIZE], ver[SIZE * 2], Next[SIZE * 2];
int dfn[SIZE], low[SIZE], n, m, tot, num, root;
bool cut[SIZE];

void add(int x, int y) {
    ver[++tot] = y;
    Next[tot] = head[x];
    head[x] = tot;
}

void tarjan(int x) {
    dfn[x] = low[x] = ++num;
    int flag = 0;
    for (int i = head[x]; i; i = Next[i]) {
        int y = ver[i];
        if (!dfn[y]) {
            tarjan(y);
            low[x] = min(low[x], low[y]);
            if (low[y] >= dfn[x]) {
                flag++;
                if (x != root || flag > 1)
                    cut[x] = true;
            }
        } else
            low[x] = min(low[x], dfn[y]);
    }
}

int main() {
    cin >> n >> m;
    tot = 1;
    for (int i = 1; i <= m; i++) {
        int x, y;
        scanf("%d%d", &x, &y);
        if (x == y)
            continue;
        add(x, y);
        add(y, x);
    }
    for (int i = 1; i <= n; i++)
        if (!dfn[i]) {
            root = i;
            tarjan(i);
        }
    for (int i = 1; i <= n; i++)
        if (cut[i])
            printf("%d ", i);
    puts("are cut-vertexes");
    return 0;
}

input:
9 11
1 2
2 3
3 4
4 5
5 1
5 2
1 6
6 9
6 8
9 8
6 7
output:
1 6 are cut-vertexes