学渣乱搞系列之Tarjan模板合集

学渣乱搞系列之Tarjan模板合集

　　　　　　　　　　　　by　狂徒归来

 

一、求强连通子图

 

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <climits>
#include <vector>
#include <queue>
#include <cstdlib>
#include <string>
#include <set>
#include <stack>
#define LL long long
#define pii pair<int,int>
#define INF 0x3f3f3f3f
using namespace std;
const int maxn = 20100;
int dfn[maxn],low[maxn],belong[maxn];
bool instack[maxn];
vector<int>g[maxn];
stack<int>stk;
int n,m,cnt,scc;
void tarjan(int u) {
    dfn[u] = low[u] = ++cnt;
    stk.push(u);
    instack[u] = true;
    for(int i = 0; i < g[u].size(); i++) {
        if(!dfn[g[u][i]]) {
            tarjan(g[u][i]);
            low[u] = min(low[u],low[g[u][i]]);
        } else if(instack[g[u][i]]) low[u] = min(low[u],dfn[g[u][i]]);
    }
    if(dfn[u] == low[u]) {
        scc++;
        int v;
        do {
            v = stk.top();
            instack[v] = false;
            belong[v] = scc;
            stk.pop();
        } while(v != u);//每一个强连通块内de点，以及其属于的scc
    }
}
int main() {
    int i,j,u,v,a,b;
    while(~scanf("%d %d",&n,&m)) {
        for(i = 0; i <= n; i++) {
            dfn[i] = belong[i] = 0;
            instack[i] = false;
            g[i].clear();
        }
        cnt = scc = 0;
        while(!stk.empty()) stk.pop();
        for(i = 1; i <= m; i++) {
            scanf("%d %d",&u,&v);
            g[u].push_back(v);
        }
        for(i = 1; i <= n; i++)
            if(!dfn[i]) tarjan(i);
    }
    return 0;
}

 

 

二、求割点

const int maxn = 1010;
vector<int>g[maxn];
bool iscut[maxn];
int dfn[maxn],low[maxn],cnt,vis[maxn];
void tarjan(int u,int fa) {
    dfn[u] = low[u] = ++cnt;
    vis[u] = 1;
    int son = 0;
    for(int i = 0; i < g[u].size(); i++) {
        if(!vis[g[u][i]]) {
            tarjan(g[u][i],u);
            son++;
            low[u] = min(low[u],low[g[u][i]]);
            if(fa == -1 && son > 1 || fa != -1 && low[g[u][i]] >= dfn[u])
                iscut[u] = true;
        } else if(vis[g[u][i]] == 1) low[u] = min(low[u],dfn[g[u][i]]);
    }
    vis[u] = 2;
}

三、求割边/桥

 

int ret;
void tarjan(int u,int fa) {
    dfn[u] = low[u] = ++clk;
    bool flag = false;
    for(int i = head[u]; ~i; i = e[i].next) {
        if(!flag && e[i].to == fa) {
            flag = true;
            continue;
        }
        if(!dfn[e[i].to]) {
            tarjan(e[i].to,u);
            low[u] = min(low[u],low[e[i].to]);
            if(low[e[i].to] > dfn[u]) {
                e[i].cut = e[i^1].cut = true;
                ++ret;
            }
        } else low[u] = min(low[u],dfn[e[i].to]);
    }
}

 

 

四、求LCA