diff --git a/algorithms-miscellaneous-4/src/main/java/com/baeldung/algorithms/smallestinteger/SmallestMissingPositiveInteger.java b/algorithms-miscellaneous-4/src/main/java/com/baeldung/algorithms/smallestinteger/SmallestMissingPositiveInteger.java
new file mode 100644
index 0000000000..b08eea2a66
--- /dev/null
+++ b/algorithms-miscellaneous-4/src/main/java/com/baeldung/algorithms/smallestinteger/SmallestMissingPositiveInteger.java
@@ -0,0 +1,37 @@
+package com.baeldung.algorithms.smallestinteger;
+
+import java.util.Arrays;
+
+public class SmallestMissingPositiveInteger {
+    public static int searchInSortedArray(int[] input) {
+        for (int i = 0; i < input.length; i++) {
+            if (i != input[i]) {
+                return i;
+            }
+        }
+
+        return input.length;
+    }
+
+    public static int searchInUnsortedArraySortingFirst(int[] input) {
+        Arrays.sort(input);
+        return searchInSortedArray(input);
+    }
+
+    public static int searchInUnsortedArrayBooleanArray(int[] input) {
+        boolean[] flags = new boolean[input.length];
+        for (int number : input) {
+            if (number < flags.length) {
+                flags[number] = true;
+            }
+        }
+
+        for (int i = 0; i < flags.length; i++) {
+            if (!flags[i]) {
+                return i;
+            }
+        }
+
+        return flags.length;
+    }
+}
diff --git a/algorithms-miscellaneous-4/src/test/java/com/baeldung/algorithms/smallestinteger/SmallestMissingPositiveIntegerUnitTest.java b/algorithms-miscellaneous-4/src/test/java/com/baeldung/algorithms/smallestinteger/SmallestMissingPositiveIntegerUnitTest.java
new file mode 100644
index 0000000000..8bb7151b41
--- /dev/null
+++ b/algorithms-miscellaneous-4/src/test/java/com/baeldung/algorithms/smallestinteger/SmallestMissingPositiveIntegerUnitTest.java
@@ -0,0 +1,88 @@
+package com.baeldung.algorithms.smallestinteger;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class SmallestMissingPositiveIntegerUnitTest {
+    @Test
+    void givenArrayWithThreeMissing_whenSearchInSortedArray_thenThree() {
+        int[] input = new int[] {0, 1, 2, 4, 5};
+
+        int result = SmallestMissingPositiveInteger.searchInSortedArray(input);
+
+        assertThat(result).isEqualTo(3);
+    }
+
+    @Test
+    void givenArrayWithOneAndThreeMissing_whenSearchInSortedArray_thenOne() {
+        int[] input = new int[] {0, 2, 4, 5};
+
+        int result = SmallestMissingPositiveInteger.searchInSortedArray(input);
+
+        assertThat(result).isEqualTo(1);
+    }
+
+    @Test
+    void givenArrayWithoutMissingInteger_whenSearchInSortedArray_thenArrayLength() {
+        int[] input = new int[] {0, 1, 2, 3, 4, 5};
+
+        int result = SmallestMissingPositiveInteger.searchInSortedArray(input);
+
+        assertThat(result).isEqualTo(input.length);
+    }
+
+    @Test
+    void givenArrayWithThreeMissing_whenSearchInUnsortedArraySortingFirst_thenThree() {
+        int[] input = new int[] {1, 4, 0, 5, 2};
+
+        int result = SmallestMissingPositiveInteger.searchInUnsortedArraySortingFirst(input);
+
+        assertThat(result).isEqualTo(3);
+    }
+
+    @Test
+    void givenArrayWithOneAndThreeMissing_whenSearchInUnsortedArraySortingFirst_thenOne() {
+        int[] input = new int[] {4, 2, 0, 5};
+
+        int result = SmallestMissingPositiveInteger.searchInUnsortedArraySortingFirst(input);
+
+        assertThat(result).isEqualTo(1);
+    }
+
+    @Test
+    void givenArrayWithoutMissingInteger_whenSearchInUnsortedArraySortingFirst_thenArrayLength() {
+        int[] input = new int[] {4, 5, 1, 3, 0, 2};
+
+        int result = SmallestMissingPositiveInteger.searchInUnsortedArraySortingFirst(input);
+
+        assertThat(result).isEqualTo(input.length);
+    }
+
+    @Test
+    void givenArrayWithThreeMissing_whenSearchInUnsortedArrayBooleanArray_thenThree() {
+        int[] input = new int[] {1, 4, 0, 5, 2};
+
+        int result = SmallestMissingPositiveInteger.searchInUnsortedArrayBooleanArray(input);
+
+        assertThat(result).isEqualTo(3);
+    }
+
+    @Test
+    void givenArrayWithOneAndThreeMissing_whenSearchInUnsortedArrayBooleanArray_thenOne() {
+        int[] input = new int[] {4, 2, 0, 5};
+
+        int result = SmallestMissingPositiveInteger.searchInUnsortedArrayBooleanArray(input);
+
+        assertThat(result).isEqualTo(1);
+    }
+
+    @Test
+    void givenArrayWithoutMissingInteger_whenSearchInUnsortedArrayBooleanArray_thenArrayLength() {
+        int[] input = new int[] {4, 5, 1, 3, 0, 2};
+
+        int result = SmallestMissingPositiveInteger.searchInUnsortedArrayBooleanArray(input);
+
+        assertThat(result).isEqualTo(input.length);
+    }
+}
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