Solution to "Count Prefix and Suffix Pairs I" problem

src/main/java/com/github/dkoval/leetcode/challenge/CountPrefixAndSuffixPairs1.java

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+package com.github.dkoval.leetcode.challenge;
+
+/**
+ * <a href="https://leetcode.com/problems/count-prefix-and-suffix-pairs-i">Count Prefix and Suffix Pairs I</a>
+ * <p>
+ * You are given a 0-indexed string array words.
+ * <p>
+ * Let's define a boolean function isPrefixAndSuffix that takes two strings, str1 and str2:
+ * <p>
+ * isPrefixAndSuffix(str1, str2) returns true if str1 is both a prefix and a suffix of str2, and false otherwise.
+ * <p>
+ * For example, isPrefixAndSuffix("aba", "ababa") is true because "aba" is a prefix of "ababa" and also a suffix, but isPrefixAndSuffix("abc", "abcd") is false.
+ * <p>
+ * Return an integer denoting the number of index pairs (i, j) such that i < j, and isPrefixAndSuffix(words[i], words[j]) is true.
+ * <p>
+ * Constraints:
+ * <ul>
+ *  <li>>1 <= words.length <= 50</li>
+ *  <li>>1 <= words[i].length <= 10</li>
+ *  <li>>words[i] consists only of lowercase English letters.</li>
+ * </ul>
+ */
+public interface CountPrefixAndSuffixPairs1 {
+
+    int countPrefixSuffixPairs(String[] words);
+
+    class CountPrefixAndSuffixPairs1Rev1 implements CountPrefixAndSuffixPairs1 {
+
+        @Override
+        public int countPrefixSuffixPairs(String[] words) {
+            final var n = words.length;
+
+            var count = 0;
+            for (var i = 0; i < n - 1; i++) {
+                for (var j = i + 1; j < n; j++) {
+                    if (isPrefixAndSuffix(words[i], words[j])) {
+                        count++;
+                    }
+                }
+            }
+            return count;
+        }
+
+        private boolean isPrefixAndSuffix(String s1, String s2) {
+            final var w1 = s1.length();
+            final var w2 = s2.length();
+
+            if (w1 > w2) {
+                return false;
+            }
+
+            for (var left = 0; left < w1; left++) {
+                if (s1.charAt(left) != s2.charAt(left)) {
+                    return false;
+                }
+
+                if (s1.charAt(w1 - left - 1) != s2.charAt(w2 - left - 1)) {
+                    return false;
+                }
+            }
+            return true;
+        }
+    }
+}

src/test/kotlin/com/github/dkoval/leetcode/challenge/CountPrefixAndSuffixPairs1Test.kt

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+package com.github.dkoval.leetcode.challenge
+
+import com.github.dkoval.leetcode.challenge.CountPrefixAndSuffixPairs1.CountPrefixAndSuffixPairs1Rev1
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Nested
+import org.junit.jupiter.api.extension.ExtensionContext
+import org.junit.jupiter.params.ParameterizedTest
+import org.junit.jupiter.params.provider.Arguments
+import org.junit.jupiter.params.provider.ArgumentsProvider
+import org.junit.jupiter.params.provider.ArgumentsSource
+import java.util.stream.Stream
+
+internal class CountPrefixAndSuffixPairs1Test {
+
+    class InputArgumentsProvider : ArgumentsProvider {
+
+        override fun provideArguments(context: ExtensionContext): Stream<out Arguments> = Stream.of(
+            Arguments.of(
+                arrayOf("a", "aba", "ababa", "aa"),
+                4
+            ),
+            Arguments.of(
+                arrayOf("pa", "papa", "ma", "mama"),
+                2
+            ),
+            Arguments.of(
+                arrayOf("abab", "ab"),
+                0
+            )
+        )
+    }
+
+    @Nested
+    inner class CountPrefixAndSuffixPairs1Rev1Test {
+
+        @ParameterizedTest
+        @ArgumentsSource(InputArgumentsProvider::class)
+        fun `should return the number of pairs and isPrefixAndSuffix(words(i), words(j)) is true`(
+            words: Array<String>,
+            expected: Int
+        ) {
+            CountPrefixAndSuffixPairs1Rev1().test(words, expected)
+        }
+    }
+}
+
+private fun CountPrefixAndSuffixPairs1.test(words: Array<String>, expected: Int) {
+    val actual = countPrefixSuffixPairs(words)
+    assertEquals(expected, actual)
+}