The weekly challenge 345 - Task 1: Peak Positions

 1 #!/usr/bin/env perl
 2 # https://theweeklychallenge.org/blog/perl-weekly-challenge-345/#TASK1
 3 #
 4 # Task 1: Peak Positions
 5 # ======================
 6 #
 7 # You are given an array of integers, @ints.
 8 #
 9 # Find all the peaks in the array, a peak is an element that is strictly
10 # greater than its left and right neighbours. Return the indices of all such
11 # peak positions.
12 #
13 ## Example 1
14 ##
15 ## Input: @ints = (1, 3, 2)
16 ## Output: (1)
17 #
18 #
19 ## Example 2
20 ##
21 ## Input: @ints = (2, 4, 6, 5, 3)
22 ## Output: (2)
23 #
24 #
25 ## Example 3
26 ##
27 ## Input: @ints = (1, 2, 3, 2, 4, 1)
28 ## Output: (2, 4)
29 #
30 #
31 ## Example 4
32 ##
33 ## Input: @ints = (5, 3, 1)
34 ## Output: (0)
35 #
36 #
37 ## Example 5
38 ##
39 ## Input: @ints = (1, 5, 1, 5, 1, 5, 1)
40 ## Output: (1, 3, 5)
41 #
42 ############################################################
43 ##
44 ## discussion
45 ##
46 ############################################################
47 #
48 # We walk from the beginning of the array to the end and check
49 # if the current element is greater than its neighbors. If so,
50 # we keep its index around to add it to the result.
51 
52 use v5.36;
53 
54 peak_positions(1, 3, 2);
55 peak_positions(2, 4, 6, 5, 3);
56 peak_positions(1, 2, 3, 2, 4, 1);
57 peak_positions(5, 3, 1);
58 peak_positions(1, 5, 1, 5, 1, 5, 1);
59 
60 sub peak_positions(@ints) {
61     say "Input: (" . join(", ", @ints) . ")";
62     my @result = ();
63     foreach my $i (0..$#ints) {
64         my $keep = 1;
65         if($i > 0) {
66             $keep = 0 if $ints[$i] <= $ints[$i-1];
67         }
68         if($i < $#ints) {
69             $keep = 0 if $ints[$i] <= $ints[$i+1];
70         }
71         push @result, $i if $keep;
72     }
73     say "Output: (" . join(", ", @result) . ")";
74 }