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+#!/usr/bin/env perl
+# https://theweeklychallenge.org/blog/perl-weekly-challenge-273/#TASK2
+#
+# Task 2: B After A
+# =================
+#
+# You are given a string, $str.
+#
+# Write a script to return true if there is at least one b, and no a appears
+# after the first b.
+#
+## Example 1
+##
+## Input: $str = "aabb"
+## Output: true
+#
+## Example 2
+##
+## Input: $str = "abab"
+## Output: false
+#
+## Example 3
+##
+## Input: $str = "aaa"
+## Output: false
+#
+## Example 4
+##
+## Input: $str = "bbb"
+## Output: true
+#
+############################################################
+##
+## discussion
+##
+############################################################
+#
+# We walk the string character for character. If we find a "b"
+# we remember this fact. If we encounter an "a" and have already
+# seen a "b", we return false. If we're at the end of the string
+# our output depends on whether or not we have seen a "b": we
+# didn't bail out for seeing an "a" after a "b", so if we didn't
+# see any "b" at all, we return false, otherwise true.
+
+use strict;
+use warnings;
+
+b_after_a("aabb");
+b_after_a("abab");
+b_after_a("aaa");
+b_after_a("bbb");
+
+sub b_after_a {
+   my $str = shift;
+   print "Input: '$str'\n";
+   my $b_seen = 0;
+   foreach my $char (split //, $str) {
+      $b_seen = 1 if $char eq "b";
+      if($b_seen) {
+         return print "Output: false\n" if $char eq "a";
+      }
+   }
+   if($b_seen) {
+      print "Output: true\n";
+   } else {
+      print "Output: false\n";
+   }
+}