kosaraju.py

#!/usr/bin/python
# -*- coding: utf-8 -*-

"""
@source: http://codehiker.wordpress.com/2012/04/06/kosarajus-scc/
I made minor changs
"""

import sys
sys.setrecursionlimit(300000)

source = 'SCC.txt'
N = 875714

# globals
visited = {}
finish = {}
leader = {}


def get_g(source):
    """ Read the Graph from a textfile """
    G = {}
    Grev = {}
    for i in range(1, N+1):
        G[i] = []
        Grev[i] = []
    fin = open(source)
    for line in fin:
        v1 = int(line.split()[0])
        v2 = int(line.split()[1])
        G[v1].append(v2)
        Grev[v2].append(v1)
    fin.close()
    return G, Grev


def init():
    for i in range(1, N+1):
        visited[i] = 0
        finish[i] = 0
        leader[i] = 0


def dfs(G, i):
    global t
    visited[i] = 1
    leader[i] = s
    for j in G[i]:
        if(visited[j] == 0):
            dfs(G, j)
    t = t + 1
    finish[i] = t


def dfs_loop(G):
    global t
    global s
    t = 0  # number of nodes processed so far
    s = 0  # current source vertex
    i = N
    while(i > 0):
        if(visited[i] == 0):
            s = i
            dfs(G, i)
        i = i-1

if __name__ == "__main__":
    init()
    g, grev = get_g()
    dfs_loop(grev)  # THE FIRST LOOP ON REVERSE GRAPH

    # construct new graph
    newGraph = {}
    for i in range(1, N+1):
        temp = []
        for x in g[i]:
            temp.append(finish[x])
        newGraph[finish[i]] = temp

    init()
    dfs_loop(newGraph)  # THE SECOND LOOP

    # statistics
    lst = sorted(leader.values())
    stat = []
    pre = 0
    for i in range(0, N-1):
        if lst[i] != lst[i+1]:
            stat.append(i + 1 - pre)
            pre = i+1
    stat.append(N-pre)
    L = sorted(stat)
    L.reverse()
    print(L[0:5])