Solution to "Counting Words With a Given Prefix" problem

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

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+package com.github.dkoval.leetcode.challenge;
+
+/**
+ * <a href="https://leetcode.com/problems/counting-words-with-a-given-prefix/">Counting Words With a Given Prefix</a>
+ * <p>
+ * You are given an array of strings words and a string pref.
+ * <p>
+ * Return the number of strings in words that contain pref as a prefix.
+ * <p>
+ * A prefix of a string s is any leading contiguous substring of s.
+ * <p>
+ * Constraints:
+ * <ul>
+ *  <li>1 <= words.length <= 100</li>
+ *  <li>1 <= words[i].length, pref.length <= 100</li>
+ *  <li>words[i] and pref consist of lowercase English letters.</li>
+ * </ul>
+ */
+public interface CountingWordsWithGivenPrefix {
+
+    int prefixCount(String[] words, String pref);
+
+    // O(W * P) time | O(1) space
+    class CountingWordsWithGivenPrefixRev1 implements CountingWordsWithGivenPrefix {
+
+        @Override
+        public int prefixCount(String[] words, String pref) {
+            var count = 0;
+            for (var word : words) {
+                if (prefix(word, pref)) {
+                    count++;
+                }
+            }
+            return count;
+        }
+
+        private boolean prefix(String word, String pref) {
+            if (word.length() < pref.length()) {
+                return false;
+            }
+
+            for (var i = 0; i < pref.length(); i++) {
+                if (word.charAt(i) != pref.charAt(i)) {
+                    return false;
+                }
+            }
+            return true;
+        }
+    }
+}

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

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+package com.github.dkoval.leetcode.challenge
+
+import com.github.dkoval.leetcode.challenge.CountingWordsWithGivenPrefix.CountingWordsWithGivenPrefixRev1
+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 CountingWordsWithGivenPrefixTest {
+
+    class InputArgumentsProvider : ArgumentsProvider {
+
+        override fun provideArguments(context: ExtensionContext): Stream<out Arguments> = Stream.of(
+            Arguments.of(
+                arrayOf("pay", "attention", "practice", "attend"),
+                "at",
+                2
+            ),
+            Arguments.of(
+                arrayOf("leetcode", "win", "loops", "success"),
+                "code",
+                0
+            )
+        )
+    }
+
+    @Nested
+    inner class CountingWordsWithGivenPrefixRev1Test {
+
+        @ParameterizedTest
+        @ArgumentsSource(InputArgumentsProvider::class)
+        fun `should Return the number of strings in words that contain pref as a prefix`(
+            words: Array<String>,
+            pref: String,
+            expected: Int
+        ) {
+            CountingWordsWithGivenPrefixRev1().test(words, pref, expected)
+        }
+    }
+}
+
+private fun CountingWordsWithGivenPrefix.test(words: Array<String>, pref: String, expected: Int) {
+    val actual = prefixCount(words, pref)
+    assertEquals(expected, actual)
+}