LaTeX-examples/presentations/ICPC-Referat/Material/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 getG(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=getG()
    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])