[JAVA-5980] First Non Repeating Character (#13072)

* [JAVA-5980] First Non Repeating Character

* [JAVA-5980] renamed UnitTest class

* [JAVA-5980] changed file location to core-java-string-algorithms-3

Co-authored-by: Bhaskar <bhaskar.dastidar@freshworks.com>

core-java-modules/core-java-string-algorithms-3/src/main/java/com/baeldung/firstnonrepeatingcharacter/FirstNonRepeatingCharacter.java

@@ -0,0 +1,72 @@
+package com.baeldung.firstnonrepeatingcharacter;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class FirstNonRepeatingCharacter {
+    public Character firstNonRepeatingCharBruteForce(String inputString) {
+        if (null == inputString || inputString.isEmpty()) {
+            return null;
+        }
+        for (Character c : inputString.toCharArray()) {
+            int indexOfC = inputString.indexOf(c);
+            if (indexOfC == inputString.lastIndexOf(c)) {
+                return c;
+            }
+        }
+        return null;
+    }
+
+    public Character firstNonRepeatingCharBruteForceNaive(String inputString) {
+        if (null == inputString || inputString.isEmpty()) {
+            return null;
+        }
+        for (int outer = 0; outer < inputString.length(); outer++) {
+            boolean repeat = false;
+            for (int inner = 0; inner < inputString.length(); inner++) {
+                if (inner != outer && inputString.charAt(outer) == inputString.charAt(inner)) {
+                    repeat = true;
+                    break;
+                }
+            }
+            if (!repeat) {
+                return inputString.charAt(outer);
+            }
+        }
+        return null;
+    }
+
+    public Character firstNonRepeatingCharWithMap(String inputString) {
+        if (null == inputString || inputString.isEmpty()) {
+            return null;
+        }
+        Map<Character, Integer> frequency = new HashMap<>();
+        for (int outer = 0; outer < inputString.length(); outer++) {
+            char character = inputString.charAt(outer);
+            frequency.put(character, frequency.getOrDefault(character, 0) + 1);
+        }
+        for (Character c : inputString.toCharArray()) {
+            if (frequency.get(c) == 1) {
+                return c;
+            }
+        }
+        return null;
+    }
+
+    public Character firstNonRepeatingCharWithArray(String inputString) {
+        if (null == inputString || inputString.isEmpty()) {
+            return null;
+        }
+        int[] frequency = new int[26];
+        for (int outer = 0; outer < inputString.length(); outer++) {
+            char character = inputString.charAt(outer);
+            frequency[character - 'a']++;
+        }
+        for (Character c : inputString.toCharArray()) {
+            if (frequency[c - 'a'] == 1) {
+                return c;
+            }
+        }
+        return null;
+    }
+}

core-java-modules/core-java-string-algorithms-3/src/test/java/com/baeldung/firstnonrepeatingcharacter/FirstNonRepeatingCharacterUnitTest.java

@@ -0,0 +1,52 @@
+package com.baeldung.firstnonrepeatingcharacter;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class FirstNonRepeatingCharacterUnitTest {
+
+    @Test
+    public void testNonRepeatingCharacterBruteForce() {
+        FirstNonRepeatingCharacter program = new FirstNonRepeatingCharacter();
+
+        Assert.assertEquals(program.firstNonRepeatingCharBruteForce("baeldung"), Character.valueOf('b'));
+        Assert.assertEquals(program.firstNonRepeatingCharBruteForce("lullaby"), Character.valueOf('u'));
+        Assert.assertEquals(program.firstNonRepeatingCharBruteForce("hello"), Character.valueOf('h'));
+        Assert.assertNull(program.firstNonRepeatingCharBruteForce("mahimahi"));
+        Assert.assertNull(program.firstNonRepeatingCharBruteForce(""));
+        Assert.assertNull(program.firstNonRepeatingCharBruteForce(null));
+    }
+
+    @Test
+    public void testNonRepeatingCharacterBruteForceNaive() {
+        FirstNonRepeatingCharacter program = new FirstNonRepeatingCharacter();
+        Assert.assertEquals(program.firstNonRepeatingCharBruteForceNaive("baeldung"), Character.valueOf('b'));
+        Assert.assertEquals(program.firstNonRepeatingCharBruteForceNaive("lullaby"), Character.valueOf('u'));
+        Assert.assertEquals(program.firstNonRepeatingCharBruteForceNaive("hello"), Character.valueOf('h'));
+        Assert.assertNull(program.firstNonRepeatingCharBruteForceNaive("mahimahi"));
+        Assert.assertNull(program.firstNonRepeatingCharBruteForceNaive(""));
+        Assert.assertNull(program.firstNonRepeatingCharBruteForceNaive(null));
+    }
+
+    @Test
+    public void testNonRepeatingCharacterWithMap() {
+        FirstNonRepeatingCharacter program = new FirstNonRepeatingCharacter();
+        Assert.assertEquals(program.firstNonRepeatingCharWithMap("baeldung"), Character.valueOf('b'));
+        Assert.assertEquals(program.firstNonRepeatingCharWithMap("lullaby"), Character.valueOf('u'));
+        Assert.assertEquals(program.firstNonRepeatingCharWithMap("hello"), Character.valueOf('h'));
+        Assert.assertNull(program.firstNonRepeatingCharWithMap("mahimahi"));
+        Assert.assertNull(program.firstNonRepeatingCharWithMap(""));
+        Assert.assertNull(program.firstNonRepeatingCharWithMap(null));
+    }
+
+    @Test
+    public void testNonRepeatingCharacterWithArray() {
+        FirstNonRepeatingCharacter program = new FirstNonRepeatingCharacter();
+        Assert.assertEquals(program.firstNonRepeatingCharWithArray("baeldung"), Character.valueOf('b'));
+        Assert.assertEquals(program.firstNonRepeatingCharWithArray("lullaby"), Character.valueOf('u'));
+        Assert.assertEquals(program.firstNonRepeatingCharWithArray("hello"), Character.valueOf('h'));
+        Assert.assertNull(program.firstNonRepeatingCharWithArray("mahimahi"));
+        Assert.assertNull(program.firstNonRepeatingCharWithArray(""));
+        Assert.assertNull(program.firstNonRepeatingCharWithArray(null));
+    }
+}