Task — Balls and boxes

There are n balls of mixed colours: red, blue or green. They are all distributed in 10 boxes labelled 0-9. You are given a $string describing the location of balls. Write a script to find the number of boxes containing all three colours. Return 0 if none found.

Examples

Example 1
Input: $str = "G0B1R2R0B0"
Output: 1
The given string describes there are 5 balls as below:
Box 0: Green(G0), Red(R0), Blue(B0) => 3 balls
Box 1: Blue(B1) => 1 ball
Box 2: Red(R2) => 1 ball

Example 2
Input: $str = "G1R3R6B3G6B1B6R1G3"
Output: 3
The given string describes there are 9 balls as below:
Box 1: Red(R1), Blue(B1), Green(G1) => 3 balls
Box 3: Red(R3), Blue(B3), Green(G3) => 3 balls
Box 6: Red(R6), Blue(B6), Green(G6) => 3 balls

Example 3
Input: $str = "B3B2G1B3"
Output: 0
Box 1: Green(G1) => 1 ball
Box 2: Blue(B2)  => 1 ball
Box 3: Blue(B3)  => 2 balls

Analysis

What is needed is to count the number of colours in each box.

I do that by setting up an array @box and ORing the value of $box[$i] by 1 if it contains a red ball, by 2 if it contains a green ball and by 4 if it contains a blue ball.

The answer is then the count of members of @box which equal 4 + 2 + 1 = 7.

The task description states that there are 10 boxes: my solution will also work if there are more (eg 'R12G12B12')

Try it 

Try running the script with any input:

Your $string =

example: R5G6B7R6G7R7

⤡

#!/usr/bin/perl

# Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge

use v5.26;    # The Weekly Challenge - 2025-03-10
use utf8;     # Week 312 - task 2 - Balls and boxes
use warnings; # Peter Campbell Smith
no warnings 'uninitialized';
binmode STDOUT, ':utf8';

balls_and_boxes('G0B1R2R0B0');
balls_and_boxes('G1R3R6B3G6B1B6R1G3');
balls_and_boxes('B3B2G1B3');

sub balls_and_boxes {
    
    my (%colours, $string, @box, $count);
    
    # initialise
    $string = shift;
    %colours = (R => 1, G => 2, B => 4);

    # count which colours seen
    $box[$2] |= $colours{$1} while $string =~ m|(.)(\d+)|g;
    
    # count full boxes
    $count = $count + ($_ == 7 ? 1 : 0) for @box;   
    
    say qq[\nInput:  \$string = '$string'];
    say qq[Output: ] . ($count + 0);
}

Output

Input:  $string = 'G0B1R2R0B0'
Output: 1

Input:  $string = 'G1R3R6B3G6B1B6R1G3'
Output: 3

Input:  $string = 'B3B2G1B3'
Output: 0