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Tower of Hanoi problem

Posted by angelheart
Sunday, April 15, 2012
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# Tower of Hanoi problem


def TowerOfHanoi(src, dest, intr, n):
if n > 0:
TowerOfHanoi(src, intr, dest, n-1)
print "Move ", src, " to ", dest
TowerOfHanoi(intr, dest, src, n-1)


n = input("Enter the number of discs : ");
TowerOfHanoi('A', 'B', 'C', n)

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Prim's Algorithm

Posted by angelheart
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# Prims algorithm


from collections import defaultdict
from heapq import *


def prim( nodes, edges ):
    conn = defaultdict( list )
    for n1,n2,c in edges:
        conn[ n1 ].append( (c, n1, n2) )
        conn[ n2 ].append( (c, n2, n1) )


    mst = []
    used = set( nodes[ 0 ] )
    usable_edges = conn[ nodes[0] ][:]
    heapify( usable_edges )


    while usable_edges:
        cost, n1, n2 = heappop( usable_edges )
        if n2 not in used:
            used.add( n2 )
            mst.append( ( n1, n2, cost ) )


            for e in conn[ n2 ]:
                if e[ 2 ] not in used:
                    heappush( usable_edges, e )
    return mst


#test
nodes = list("ABCDEFG")
edges = [ ("A", "B", 7), ("A", "D", 5),
          ("B", "C", 8), ("B", "D", 9), 
 ("B", "E", 7), ("C", "E", 5),
 ("D", "E", 15), ("D", "F", 6),
 ("E", "F", 8), ("E", "G", 9),
 ("F", "G", 11)]


print "prim:", prim( nodes, edges )

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N Queens Problem using Backtracking

Posted by angelheart
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#N Queens problem using Backtracking


x = {}
def nqueen(k, n):
for i in range(1, n+1):
if place(k, i):
x[k] = i
if k == n:
print x
else:
nqueen(k+1, n)


def place(row, col):
for j in range(1, row):
if x[j] == col or abs(j-row) == abs(x[j]-col):
return False
return True


n = input("Enter the number of queens : ")
nqueen(1, n)

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Learn Python

Posted by angelheart
Friday, December 9, 2011
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Python is an easy to learn, powerful programming language. It has efficient high-level data structures and a simple but effective approach to object-oriented programming. Python’s elegant syntax and dynamic typing, together with its interpreted nature, make it an ideal language for scripting and rapid application development in many areas on most platforms.


Learn Python (Web Link)

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