Shortest distance

You are given a string and a character in the given string. Write a script to return an array of integers of size same as length of the given string such that distance[i] is the distance from index i to the closest occurence of the given character in the given string. The distance between two indices i and j is abs(i - j).

Examples

Example 1
Input: $str = "loveleetcode", $char = "e"
Output: (3,2,1,0,1,0,0,1,2,2,1,0)

The character 'e' appears at indices 3, 5, 6, and 11 
(0-indexed). The closest occurrence of 'e' for index 0 
is at index 3, so the distance is abs(0 - 3) = 3. The 
closest occurrence of 'e' for index 1 is at index 3, 
so the distance is abs(1 - 3) = 2.

For index 4, there is a tie between the 'e' at index 3
and the 'e' at index 5, but the distance is still the 
same: abs(4 - 3) == abs(4 - 5) = 1.

The closest occurrence of 'e' for index 8 is at index 6, 
so the distance is abs(8 - 6) = 2.

Example 2
Input: $str = "aaab", $char = "b"
Output: (3,2,1,0)

Analysis

I feel sure someone will come up with a one-liner, but I chose simply to pass twice along the string, once forwards and once backwards, setting a counter to zero every time I met a $char and incrementing it when I didn't.

For each string position, the desired result is the smaller of the counter value going forwards or backwards.

Simple loop over can be good enough as shown in this week solutions. Thanks for sharing.

Try it 

#!/usr/bin/perl

use v5.26;    # The Weekly Challenge - 2023-12-18
use utf8;     # Week 248 task 1 - Shortest distance
use strict;   # Peter Campbell Smith
use warnings; # Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge

shortest_distance('loveleetcode', 'e');
shortest_distance('We wish you a merry christmas and a happy new year!', 'a');
shortest_distance('zoos contain animals', 'z');
shortest_distance('tornadoes have a vortex', 'x');
shortest_distance('xylophones and zithers', 'q');

sub shortest_distance {
    
    my ($string, $char, @letters, $last, @count, @dist, $j, $count, $i, $k);
    
    ($string, $char) = @_;
    
    # initialise
    @letters = split('', $string);
    $last = @letters - 1;
    $dist[$_] = 999 for 0 .. $last;
    $count = 999;
    
    # go along string forwards and backwards
    for $k (0, 1) {
        for $j (0 .. $last) {
            $i = $k ? $j : $last - $j;
            
            # if we've found a $char reset count to 0
            if ($letters[$i] eq $char) {
                $count = $dist[$i] = 0;
                
            # or save the distance to the nearest $char 
            } else {
                $count ++;
                $dist[$i] = $count if $count < $dist[$i];
            }
        }
    }
    say qq[\nInput:  \@string = '$string', \$char = '$char'];
    say qq[Output: ] . ($dist[0] != 999 ? join(', ', @dist) : qq['$char' does not occur in '$string']); 
}

17 lines of code

Output from script

Input:  @string = 'loveleetcode', $char = 'e'
Output: 3, 2, 1, 0, 1, 0, 0, 1, 2, 2, 1, 0

Input:  @string = 'We wish you a merry christmas and a happy new year!', $char = 'a'
Output: 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 1, 2, 3, 4, 5, 6, 7, 7, 6, 5, 4, 3, 2, 1, 0, 1, 1, 0, 1, 2, 1, 0, 1, 1, 0, 1, 2, 3, 4, 5, 5, 4, 3, 2, 1, 0, 1, 2

Input:  @string = 'zoos contain animals', $char = 'z'
Output: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19

Input:  @string = 'tornadoes have a vortex', $char = 'x'
Output: 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0

Input:  @string = 'xylophones and zithers', $char = 'q'
Output: 'q' does not occur in 'xylophones and zithers'