Irhad Fejzic Irhad Fejzic - 1 year ago 124
Python Question

Odds of coin flipping heads 10 times in a row

I can easily find the number of heads out of 100 and the chances of coin flipping heads out of 100 flips. That code is below. However, I can't figure out how to easily get the odds of coin flipping heads 10 times in a row.

import random

n = int(input("Enter the number of flips: "))

sum = 0
heads = 0
tails = 0
for n in range(1, n + 1):
number = random.randrange(0,2)
if number == 0:
heads += 1
tails += 1
sum += number
odds = sum / n

print("No. of heads: ", heads)
print("No. of tails: ", tails)
print("Odds: ", odds)

Answer Source

You need to flip the coin 10 times, but only report success if they all come up heads. Do this with reverse logic: if any one comes up tails, set your flag to False.

all_heads = True
for i in range(10):
    number = random.randrange(0,2)
    if number != 0:
        all_heads = False

Or, more succinctly

all_heads = True
for i in range(10):
    all_heads &= random.randrange(0,2) == 0

... and even more pythonic

all_heads = all(random.randrange(0,2) == 0 for i in range(10))

Whichever you choose, you'll need to do it enough times to approximate a statistical universe. Since you expect only one success in 1024 trials, you'll want on the order of 10,000 - 100,000 trials. Count the number of successes, divide by the number of trials. You already know how to do that part.


Given the length of the run of heads, n, and the number of trials, this reduces to

print (sum(all(random.randrange(0,2) for _ in range(n)) \
          for _ in range(trials))                       \
       / float(trials) )

Welcome to Python. :-)

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