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#-----------------------------------------------------------------------

# selfavoid.py

#-----------------------------------------------------------------------

import stdio

import stdarray

import sys

import random

# Accept integers n and trialCount as command-line arguments. Do

# trialCount random self-avoiding walks in an n-by-n lattice.

# Write to standard output the percentage of dead ends encountered.

n = int(sys.argv[1])

trials = int(sys.argv[2])

deadEnds = 0

for t in range(trials):

# Create an n-by-n array, with all elements set to False.

a = stdarray.create2D(n, n, False)

x = n//2

y = n//2

while (x > 0) and (x < n-1) and (y > 0) and (y < n-1):

# Check for dead end and make a random move.

a[x][y] = True

if a[x-1][y] and a[x+1][y] and a[x][y-1] and a[x][y+1]:

deadEnds += 1

break

r = random.randrange(1, 5)

if (r == 1) and (not a[x+1][y]):

x += 1

elif (r == 2) and (not a[x-1][y]):

x -= 1

elif (r == 3) and (not a[x][y+1]):

y += 1

elif (r == 4) and (not a[x][y-1]):

y -= 1

stdio.writeln(str(100*deadEnds//trials) + '% dead ends')

#-----------------------------------------------------------------------

# python selfavoid.py 5 100

# 0% dead ends

# python selfavoid.py 20 100

# 27% dead ends

# python selfavoid.py 40 100

# 80% dead ends

# python selfavoid.py 80 100

# 96% dead ends

# python selfavoid.py 5 1000

# 0% dead ends

# python selfavoid.py 20 1000

# 33% dead ends

# python selfavoid.py 40 1000

# 77% dead ends

# python selfavoid.py 80 1000

# 98% dead ends