BAEL-7328: Find All Missing Numbers From a Given Array in Java (#15443)

Co-authored-by: Tapan Avasthi <tavasthi@Tapans-MacBook-Air.local>

algorithms-modules/algorithms-miscellaneous-7/src/test/java/com/baeldung/algorithms/findmissingnumber/FindMissingNumberUnitTest.java

@@ -0,0 +1,84 @@
+package com.baeldung.algorithms.findmissingnumber;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Arrays;
+import java.util.BitSet;
+import java.util.stream.IntStream;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class FindMissingNumberUnitTest {
+
+    private int[] numbers;
+    int N;
+
+    @BeforeEach
+    void setup() {
+        numbers = new int[] { 1, 4, 5, 2, 7, 8, 6, 9 };
+        N = numbers.length + 1;
+    }
+
+    @Test
+    void givenIntegersArray_whenUseArithmeticSumToFindMissingNumber_thenGetMissingNumber() {
+        int expectedSum = (N * (N + 1)) / 2;
+        int actualSum = Arrays.stream(numbers).sum();
+
+        int missingNumber = expectedSum - actualSum;
+        assertEquals(3, missingNumber);
+    }
+
+    @Test
+    void givenIntegersArray_whenUseXorToFindMissingNumber_thenGetMissingNumber() {
+        int xorValue = IntStream.rangeClosed(1, N).reduce(0, (a, b) -> a ^ b);
+
+        xorValue = Arrays.stream(numbers).reduce(xorValue, (x, y) -> x ^ y);
+
+        assertEquals(3, xorValue);
+    }
+
+    @Test
+    void givenIntegersArray_whenUseSortingToFindMissingNumber_thenGetMissingNumber() {
+        Arrays.sort(numbers);
+
+        int missingNumber = -1;
+        for (int index = 0; index < numbers.length; index++) {
+            if (numbers[index] != index + 1) {
+                missingNumber = index + 1;
+                break;
+            }
+        }
+
+        assertEquals(3, missingNumber);
+    }
+
+    @Test
+    void givenIntegersArray_whenTrackUsingBooleanArrayToFindMissingNumber_thenGetMissingNumber() {
+        boolean[] present = new boolean[N];
+
+        int missingNumber = -1;
+        Arrays.stream(numbers).forEach(number -> present[number - 1] = true);
+
+        for (int index = 0; index < present.length; index++) {
+            if (!present[index]) {
+                missingNumber = index + 1;
+                break;
+            }
+        }
+
+        assertEquals(3, missingNumber);
+    }
+
+    @Test
+    void givenIntegersArray_whenUseBitSetToFindMissingNumber_thenGetMissingNumber() {
+        BitSet bitSet = new BitSet(N);
+        for (int num : numbers) {
+            bitSet.set(num);
+        }
+
+        int missingNumber = bitSet.nextClearBit(1);
+
+        assertEquals(3, missingNumber);
+    }
+}