Hi people, I'm trying to figure out what's wrong with my code. My goal is to calculate the average number of stones it takes so that 2 stones become adjascent on a 19x19 goban (the board of the game of go), when we randomly pick an intersection and place a stone on it. The answer should be almost 13 if I remember well. Here's my code: Code (Python): # Program that estimates the average number of stones required so that 2 stones # become adjascent in an nxn goban. I want to plot the distribution of number # of stones vs numbers of trial, i.e. an histogram. import random import numpy as np # Size of the board n = 19 # Number of trials trials = 1000 # Initialize the board list of lists to 0. 0 means no stone, 1 means stone. # Note that board is the first element and board is the last one # , for when n=19. That's because I define the board # as n+2 x n+2 for the edges... board = [*(n+2) for i in range(n+2)] counter = 0 # Generate random coordinates inside of the 19x19 board x_coordinates, y_coordinates = random.randint(1, n), random.randint(1, n) # Now define a boolean function that I'll use as a condition in a while loop def check_if_stones(x_coordinates, y_coordinates): if (board[x_coordinates-1][y_coordinates] == 1 or board[x_coordinates][y_coordinates-1] == 1 or board[x_coordinates+1][y_coordinates] == 1 or board[x_coordinates][y_coordinates+1] == 1): return False else: return True trial_list =  for j in range(trials): while check_if_stones(x_coordinates, y_coordinates): if board[x_coordinates][y_coordinates] == 0: # Now replace a random element by 1 board[x_coordinates][y_coordinates] = 1 counter += 1 x_coordinates, y_coordinates = random.randint(1, n), random.randint(1, n) x_coordinates, y_coordinates = random.randint(1, n), random.randint(1, n) # Update the counter when the boolean function returns false. Do this outside of the while loop. counter += 1 trial_list.append(counter) x_coordinates, y_coordinates = random.randint(1, n), random.randint(1, n) print(np.mean(trial_list)) Now, when trials = 1000 like in the code, one would expect the result to be close to 13. But it returns a number around 622. When trial is worth 5 I get an output of around 17... So that np.mean(trial_list) depends heavily on "trials" while it shouldn't depend that heavily on it. I've no idea what's wrong with the code and I'm desperate to fix it. I'd appreciate if you could spot anything weird, thanks! P.D.:Sorry about the indentation, it seems to be broken when I paste it from Emacs. I've edited it manually but I may have goofed here on PF somewhere.