Task — Root distance

You are given a tree and a node of the given tree. Write a script to find out the distance of the given node from the root.

Examples

Example 1:
Tree:
        1
       / \
      2   3
           \
            4
           / \
          5   6
Node: 6
Output: 3 as the distance of given node 6 from the 
   root (1).
Node: 5
Output: 3
Node: 2
Output: 1
Node: 4
Output: 2

Example 2:
Tree:
        1
       / \
      2   3
     /     \
    4       5
     \     /
      6   7
     / \
    8   9
Node: 7
Output: 3 as the distance of given node 6 from the 
   root (1).
Node: 8
Output: 4
Node: 6
Output: 3

Analysis

I did not submit a solution at the time, but have written this later

The first issue is how to represent the tree. I have chosen to input it as a series of $parent, $child arrays, with the notional parent of the root being 0.

It is then just a case of starting with the given node, and counting back to the parent and its parent and so on to the root.

Try it 

#!/usr/bin/perl

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

use v5.26;    # The Weekly Challenge - 2021-09-06
use utf8;     # Week 129 - task 1 - Root distance
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';

root_distance([6, 5, 2, 4], [0, 1], [1, 2], [1, 3], [3, 4], [4, 5], [4, 6]);
root_distance([7, 8, 6], [0, 1], [1, 2], [1, 3], [2, 4], [3, 5], [4, 6], [5, 7], [6, 8], [6, 9]);

sub root_distance {
    
    my (@input, $given, $j, $k, %node, $count, $parents, $nodes);
    
    # process input
    @input = @_;
    $nodes = shift @input;
    
    for $k (@input) {
        $node{$k->[1]} = $k->[0];
        $parents .= qq[$k->[0]→$k->[1], ];
    }
    
    # loop back from each supplied node to the root
    for $j (@$nodes) {
        $count = 0;
        $k = $j;
        while (1) {
            last if $node{$k} == 0;
            $k = $node{$k};
            $count ++;
        }
        printf(qq[\nInput:  \$node = %s, \@children = %s\n], $j, substr($parents, 5, -2));
        printf(qq[Output: %s\n], $count);
    }
}

Output

Input:  $node = 6, @children = 1→2, 1→3, 3→4, 4→5, 4→6
Output: 3

Input:  $node = 5, @children = 1→2, 1→3, 3→4, 4→5, 4→6
Output: 3

Input:  $node = 2, @children = 1→2, 1→3, 3→4, 4→5, 4→6
Output: 1

Input:  $node = 4, @children = 1→2, 1→3, 3→4, 4→5, 4→6
Output: 2

Input:  $node = 7, @children = 1→2, 1→3, 2→4, 3→5, 4→6, 
   5→7, 6→8, 6→9
Output: 3

Input:  $node = 8, @children = 1→2, 1→3, 2→4, 3→5, 4→6, 
   5→7, 6→8, 6→9
Output: 4

Input:  $node = 6, @children = 1→2, 1→3, 2→4, 3→5, 4→6, 
   5→7, 6→8, 6→9
Output: 3