AlgorithmLibrary/SCC.cpp at master · bluecoffee8/AlgorithmLibrary · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
/**
 * Author: Kevin Li
 * Lang: C++
 * Description: finds Strongly Connected Components via Tarjan method, also calculates the kernel DAG
 */

#include <iostream>
#include <vector>
#include <unordered_set>
#include <set>
using namespace std;
#define pb push_back
#define mp make_pair
#define f first
#define s second
typedef pair<int,int> pi;

struct scc {
    int n;
    vector<int> *e;
    int *low, *num;
    vector<int> vst;
    vector<int> *cmp;
    int dfsnum, numscc;
    bool *vis;

    int *sccmap;

    unordered_set<int> *kdags;
    vector<int> *kdag;

    scc () {}
    scc (int _n) : n(_n) {
        e = new vector<int>[n];
        low = new int[n];
        num = new int[n];
        cmp = new vector<int>[n];
        vis = new bool[n];
        numscc = dfsnum = 0;
        sccmap = new int[n];
    }
    void add(int u, int v) {
        e[u].pb(v);
    }
    void dfs(int node) {
        low[node] = num[node] = dfsnum;
        dfsnum++;
        vis[node] = true;
        vst.pb(node);
        for (int i = 0; i < e[node].size(); i++) {
            if (num[e[node][i]] == 0) {
                dfs(e[node][i]);
                low[node] = min(low[node],low[e[node][i]]);
            }
            else if (vis[e[node][i]] == true) {
                low[node] = min(low[node],num[e[node][i]]);
            }
        }
        if (low[node] == num[node]) {
            while (true) {
                int vertex = vst.back();
                vst.pop_back();
                vis[vertex] = false;
                cmp[numscc].pb(vertex);
                if (vertex == node) {
                    break;
                }
            }
            numscc++;
        }
    }
    void driver() {
        numscc = 0;
        dfsnum = 1;
        for (int i = 0; i < n; i++) {
            low[i] = num[i] = 0;
            vis[i] = false;
        }
        for (int i = 0; i < n; i++) {
            if (num[i] == 0) {
                dfs(i);
            }
        }
    }

    void kerneldag() {
        kdags = new unordered_set<int>[n];
        kdag = new vector<int>[n];
        for (int i = 0; i < numscc; i++) {
            for (int j = 0; j < cmp[i].size(); j++) {
                sccmap[cmp[i][j]] = i;
            }
        }
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < e[i].size(); j++) {
                if (sccmap[i] != sccmap[e[i][j]]) {
                    kdags[sccmap[i]].insert(sccmap[e[i][j]]);
                }
            }
        }
        for (int i = 0; i < numscc; i++) {
            for (auto j = kdags[i].begin(); j != kdags[i].end(); j++) {
                kdag[i].pb(*j);
            }
        }
    }
    void print() {
        for (int i = 0; i < numscc; i++) {
            for (int j = 0; j < cmp[i].size(); j++) {
                cout << cmp[i][j] << " ";
            }
            cout << endl;
        }
        cout << endl;
    }
    void printdag() {
        for (int i = 0; i < numscc; i++) {
            for (int j = 0; j < kdag[i].size(); j++) {
                cout << kdag[i][j] << " ";
            }
            cout << endl;
        }
        cout << endl;
    }
};

int n,m;

int main() {
    cin >> n >> m;
    scc SCC = scc(n);
    for (int i = 0; i < m; i++) {
        int u,v; cin >> u >> v;
        SCC.add(u,v);
    }
    SCC.driver();
    // SCC.kerneldag();
    SCC.print();
    // SCC.printdag();
}