The weekly challenge 349 - Task 2: Meeting Point

  1 #!/usr/bin/env perl
  2 # https://theweeklychallenge.org/blog/perl-weekly-challenge-349/#TASK2
  3 #
  4 # Task 2: Meeting Point
  5 # =====================
  6 #
  7 # You are given instruction string made up of U (up), D (down), L (left) and R
  8 # (right).
  9 #
 10 # Write a script to return true if following the instruction, you meet (0,0) at
 11 # any point along the sequence.
 12 #
 13 ## Example 1
 14 ##
 15 ## Input: $path = "ULD"
 16 ## Output: false
 17 ##
 18 ## (-1,1) <- (0,1)
 19 ##    |        ^
 20 ##    v        |
 21 ## (-1,0)    (0,0)
 22 #
 23 #
 24 ## Example 2
 25 ##
 26 ## Input: $path = "ULDR"
 27 ## Output: true
 28 ##
 29 ##  (-1,1) <- (0,1)
 30 ##     |        ^
 31 ##     v        |
 32 ##  (-1,0) -> (0,0)
 33 #
 34 #
 35 ## Example 3
 36 ##
 37 ## Input: $path = "UUURRRDDD"
 38 ## Output: false
 39 ##
 40 ## (0,3) -> (1,3) -> (2,3) -> (3,3)
 41 ##   ^                          |
 42 ##   |                          v
 43 ## (0,2)                      (3,2)
 44 ##   ^                          |
 45 ##   |                          v
 46 ## (0,1)                      (3,1)
 47 ##   ^                          |
 48 ##   |                          v
 49 ## (0,0)                      (3,0)
 50 #
 51 #
 52 ## Example 4
 53 ##
 54 ## Input: $path = "UURRRDDLLL"
 55 ## Output: true
 56 ##
 57 ## (0,2) -> (1,2) -> (2,2) -> (3,2)
 58 ##   ^                          |
 59 ##   |                          v
 60 ## (0,1)                      (3,1)
 61 ##   ^                          |
 62 ##   |                          v
 63 ## (0,0) <- (1,0) <- (1,1) <- (3,0)
 64 #
 65 #
 66 ## Example 5
 67 ##
 68 ## Input: $path = "RRUULLDDRRUU"
 69 ## Output: true
 70 ##
 71 ## (0,2) <- (1,2) <- (2,2)
 72 ##   |                 ^
 73 ##   v                 |
 74 ## (0,1)             (2,1)
 75 ##   |                 ^
 76 ##   v                 |
 77 ## (0,0) -> (1,0) -> (2,1)
 78 #
 79 ############################################################
 80 ##
 81 ## discussion
 82 ##
 83 ############################################################
 84 #
 85 # We walk the path and check where we are. If we are back to
 86 # (0, 0) at any time during the walk, we can return true already.
 87 # In the end, if we didn't return true at some point, we can
 88 # return false.
 89 #
 90 use v5.36;
 91 
 92 meeting_point("ULD");
 93 meeting_point("ULDR");
 94 meeting_point("UUURRRDDD");
 95 meeting_point("UURRRDDLLL");
 96 meeting_point("RRUULLDDRRUU");
 97 
 98 sub meeting_point($path) {
 99     say "Input: '$path'";
100     my ($x, $y) = (0, 0);
101     foreach my $step (split //, $path) {
102         if($step eq "U") {
103             $y++;
104         } elsif ($step eq "D") {
105             $y--;
106         } elsif ($step eq "L") {
107             $x--;
108         } else {
109             $x++;
110         }
111         say "($x, $y)";
112         if($x == 0 and $y == 0) {
113             return say "Output: true";
114         }
115     }
116     say "Output: false";
117 }
118