-
Notifications
You must be signed in to change notification settings - Fork 0
/
Kosaraju's Algorithm.cpp
91 lines (85 loc) · 2.33 KB
/
Kosaraju's Algorithm.cpp
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
#include <iostream>
#include <vector>
#include <stack>
using namespace std;
// topological sort using DFS
void topoSort(vector<vector<int>> &adjList, int node, vector<bool> &visited, stack<int> &st)
{
visited[node] = true;
int neighours = adjList[node].size();
for (int i = 0; i < neighours; i++)
{
int neighourNode = adjList[node][i];
if (!visited[neighourNode])
{
topoSort(adjList, neighourNode, visited, st);
}
}
st.push(node);
}
void revDfs(int node, vector<bool> &visited, vector<vector<int>> &transpose)
// DFS from the topological stack order
{
cout << node << " ";
visited[node] = true;
int neighours = transpose[node].size();
for (int i = 0; i < neighours; i++)
{
int neighourNode = transpose[node][i];
if (!visited[neighourNode])
{
revDfs(neighourNode, visited, transpose);
}
}
}
void Kosaraju(vector<vector<int>> &adjList, int n)
{
vector<bool> visited(n, false);
stack<int> st; // for topological sort
for (int i = 0; i < n; i++) // if the graph has multiple components
{
if (!visited[i])
{
topoSort(adjList, i, visited, st);
}
}
vector<vector<int>> transpose(n); // declaring a new matrix to store transpose
for (int i = 0; i < n; i++)
{
visited[i] = false;
int neighours = adjList[i].size();
for (int j = 0; j < neighours; j++)
{
int neighourNode = adjList[i][j];
transpose[neighourNode].push_back(i);
}
}
while (!st.empty())
{
int node = st.top();
st.pop();
if (!visited[node])
{
cout << "SCC: ";
revDfs(node, visited, transpose);
cout << endl;
}
}
}
void add_edge(vector<vector<int>> &adjList, int u, int v)
{
adjList[u].push_back(v); // Kosaraju's algorithm is used for only directed graphs
}
int main()
{
int n = 6;
vector<vector<int>> adjList(n); // using a vector of vector of pairs to store weights
add_edge(adjList, 0, 2); // means there is an edge from 0 to 1 with a weight 2
add_edge(adjList, 2, 1);
add_edge(adjList, 1, 0);
add_edge(adjList, 2, 4);
add_edge(adjList, 4, 3);
add_edge(adjList, 3, 5);
add_edge(adjList, 5, 4);
Kosaraju(adjList, n);
}