diff --git a/src/main/java/com/thealgorithms/slidingwindow/LongestSubstringWithoutRepeatingCharacters.java b/src/main/java/com/thealgorithms/slidingwindow/LongestSubstringWithoutRepeatingCharacters.java
new file mode 100644
index 000000000000..0641730d8b09
--- /dev/null
+++ b/src/main/java/com/thealgorithms/slidingwindow/LongestSubstringWithoutRepeatingCharacters.java
@@ -0,0 +1,46 @@
+package com.thealgorithms.slidingwindow;
+import java.util.HashSet;
+
+/**
+ * The Longest Substring Without Repeating Characters algorithm finds the length of
+ * the longest substring without repeating characters in a given string.
+ *
+ * <p>
+ * Worst-case performance O(n)
+ * Best-case performance O(n)
+ * Average performance O(n)
+ * Worst-case space complexity O(min(n, m)), where n is the length of the string
+ * and m is the size of the character set.
+ *
+ * @author  (https://github.com/Chiefpatwal)
+ */
+public final class LongestSubstringWithoutRepeatingCharacters {
+
+    // Prevent instantiation
+    private LongestSubstringWithoutRepeatingCharacters() {
+    }
+
+    /**
+     * This method finds the length of the longest substring without repeating characters.
+     *
+     * @param s is the input string
+     * @return the length of the longest substring without repeating characters
+     */
+    public static int lengthOfLongestSubstring(String s) {
+        int maxLength = 0;
+        int left = 0;
+        HashSet<Character> charSet = new HashSet<>();
+
+        for (int right = 0; right < s.length(); right++) {
+            // If the character is already in the set, remove characters from the left
+            while (charSet.contains(s.charAt(right))) {
+                charSet.remove(s.charAt(left));
+                left++;
+            }
+            charSet.add(s.charAt(right));
+            maxLength = Math.max(maxLength, right - left + 1);
+        }
+
+        return maxLength;
+    }
+}
diff --git a/src/main/java/com/thealgorithms/slidingwindow/MaxSumKSizeSubarray.java b/src/main/java/com/thealgorithms/slidingwindow/MaxSumKSizeSubarray.java
new file mode 100644
index 000000000000..7e8095e08a0b
--- /dev/null
+++ b/src/main/java/com/thealgorithms/slidingwindow/MaxSumKSizeSubarray.java
@@ -0,0 +1,50 @@
+package com.thealgorithms.slidingwindow;
+
+/**
+ * The Sliding Window algorithm is used to find the maximum sum of a subarray
+ * of a fixed size k within a given array.
+ *
+ * <p>
+ * Worst-case performance O(n)
+ * Best-case performance O(n)
+ * Average performance O(n)
+ * Worst-case space complexity O(1)
+ *
+ * @author Your Name (https://github.com/Chiefpatwal)
+ */
+public final class MaxSumKSizeSubarray {
+
+    // Prevent instantiation
+    private MaxSumKSizeSubarray() {
+    }
+
+    /**
+     * This method finds the maximum sum of a subarray of a given size k.
+     *
+     * @param arr is the input array where the maximum sum needs to be found
+     * @param k   is the size of the subarray
+     * @return the maximum sum of the subarray of size k
+     */
+    public static int maxSumKSizeSubarray(int[] arr, int k) {
+        if (arr.length < k) {
+            return -1; // Edge case: not enough elements
+        }
+
+        int maxSum;
+        int windowSum = 0;
+
+        // Calculate the sum of the first window
+        for (int i = 0; i < k; i++) {
+            windowSum += arr[i];
+        }
+        maxSum = windowSum;
+
+        // Slide the window across the array
+        for (int i = k; i < arr.length; i++) {
+            windowSum += arr[i] - arr[i - k];
+            maxSum = Math.max(maxSum, windowSum);
+        }
+
+        return maxSum;
+    }
+}
diff --git a/src/main/java/com/thealgorithms/slidingwindow/MinimumConsecutiveCards.java b/src/main/java/com/thealgorithms/slidingwindow/MinimumConsecutiveCards.java
new file mode 100644
index 000000000000..02bcc396bcb9
--- /dev/null
+++ b/src/main/java/com/thealgorithms/slidingwindow/MinimumConsecutiveCards.java
@@ -0,0 +1,44 @@
+package com.thealgorithms.slidingwindow;
+
+import java.util.HashMap;
+
+/**
+ * The MinimumConsecutiveCards algorithm finds the minimum number of consecutive cards
+ * that need to be picked up to get a pair of the same card.
+ *
+ * <p>
+ * Worst-case performance O(n)
+ * Best-case performance O(n)
+ * Average performance O(n)
+ * Worst-case space complexity O(n)
+ *
+ * @author  (https://github.com/Chiefpatwal)
+ */
+public final class MinimumConsecutiveCards {
+
+    // Prevent instantiation
+    private MinimumConsecutiveCards() {
+    }
+
+    /**
+     * This method finds the minimum number of consecutive cards needed to be picked up
+     * to get a pair of the same card.
+     *
+     * @param cards an array of integers representing card numbers
+     * @return the minimum number of consecutive cards to pick up, or -1 if no pairs exist
+     */
+    public static int minimumCardPickup(int[] cards) {
+        HashMap<Integer, Integer> cardIndexMap = new HashMap<>();
+        int minLength = Integer.MAX_VALUE;
+
+        for (int i = 0; i < cards.length; i++) {
+            if (cardIndexMap.containsKey(cards[i])) {
+                int prevIndex = cardIndexMap.get(cards[i]);
+                minLength = Math.min(minLength, i - prevIndex + 1);
+            }
+            cardIndexMap.put(cards[i], i);
+        }
+
+        return minLength == Integer.MAX_VALUE ? -1 : minLength;
+    }
+}
diff --git a/src/test/java/com/thealgorithms/slidingwindow/LongestSubstringWithoutRepeatingCharactersTest.java b/src/test/java/com/thealgorithms/slidingwindow/LongestSubstringWithoutRepeatingCharactersTest.java
new file mode 100644
index 000000000000..8638a707a3e2
--- /dev/null
+++ b/src/test/java/com/thealgorithms/slidingwindow/LongestSubstringWithoutRepeatingCharactersTest.java
@@ -0,0 +1,23 @@
+package com.thealgorithms.slidingwindow;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the LongestSubstringWithoutRepeatingCharacters class.
+ *
+ * @author  (https://github.com/Chiefpatwal)
+ */
+public class LongestSubstringWithoutRepeatingCharactersTest {
+
+    @Test
+    public void testLengthOfLongestSubstring() {
+        // Test cases for the lengthOfLongestSubstring method
+        assertEquals(3, LongestSubstringWithoutRepeatingCharacters.lengthOfLongestSubstring("abcabcbb"));
+        assertEquals(1, LongestSubstringWithoutRepeatingCharacters.lengthOfLongestSubstring("bbbbb"));
+        assertEquals(3, LongestSubstringWithoutRepeatingCharacters.lengthOfLongestSubstring("pwwkew"));
+        assertEquals(0, LongestSubstringWithoutRepeatingCharacters.lengthOfLongestSubstring(""));
+        assertEquals(5, LongestSubstringWithoutRepeatingCharacters.lengthOfLongestSubstring("abcde"));
+    }
+}
diff --git a/src/test/java/com/thealgorithms/slidingwindow/MaxSumKSizeSubarrayTest.java b/src/test/java/com/thealgorithms/slidingwindow/MaxSumKSizeSubarrayTest.java
new file mode 100644
index 000000000000..aa3c2eae3294
--- /dev/null
+++ b/src/test/java/com/thealgorithms/slidingwindow/MaxSumKSizeSubarrayTest.java
@@ -0,0 +1,79 @@
+package com.thealgorithms.slidingwindow;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the MaxSumKSizeSubarray class.
+ *
+ * @author Your Name (https://github.com/Chiefpatwal)
+ */
+class MaxSumKSizeSubarrayTest {
+
+    /**
+     * Test for the basic case of finding the maximum sum.
+     */
+    @Test
+    void testMaxSumKSizeSubarray() {
+        int[] arr = {1, 2, 3, 4, 5};
+        int k = 2;
+        int expectedMaxSum = 9; // 4 + 5
+        assertEquals(expectedMaxSum, MaxSumKSizeSubarray.maxSumKSizeSubarray(arr, k));
+    }
+
+    /**
+     * Test for a different array and subarray size.
+     */
+    @Test
+    void testMaxSumKSizeSubarrayWithDifferentValues() {
+        int[] arr = {2, 1, 5, 1, 3, 2};
+        int k = 3;
+        int expectedMaxSum = 9; // 5 + 1 + 3
+        assertEquals(expectedMaxSum, MaxSumKSizeSubarray.maxSumKSizeSubarray(arr, k));
+    }
+
+    /**
+     * Test for edge case with insufficient elements.
+     */
+    @Test
+    void testMaxSumKSizeSubarrayWithInsufficientElements() {
+        int[] arr = {1, 2};
+        int k = 3; // Not enough elements
+        int expectedMaxSum = -1; // Edge case
+        assertEquals(expectedMaxSum, MaxSumKSizeSubarray.maxSumKSizeSubarray(arr, k));
+    }
+
+    /**
+     * Test for large array.
+     */
+    @Test
+    void testMaxSumKSizeSubarrayWithLargeArray() {
+        int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
+        int k = 5;
+        int expectedMaxSum = 40; // 6 + 7 + 8 + 9 + 10
+        assertEquals(expectedMaxSum, MaxSumKSizeSubarray.maxSumKSizeSubarray(arr, k));
+    }
+
+    /**
+     * Test for array with negative numbers.
+     */
+    @Test
+    void testMaxSumKSizeSubarrayWithNegativeNumbers() {
+        int[] arr = {-1, -2, -3, -4, -5};
+        int k = 2;
+        int expectedMaxSum = -3; // -1 + -2
+        assertEquals(expectedMaxSum, MaxSumKSizeSubarray.maxSumKSizeSubarray(arr, k));
+    }
+
+    /**
+     * Test for the case where k equals the array length.
+     */
+    @Test
+    void testMaxSumKSizeSubarrayWithKEqualToArrayLength() {
+        int[] arr = {1, 2, 3, 4, 5};
+        int k = 5;
+        int expectedMaxSum = 15; // 1 + 2 + 3 + 4 + 5
+        assertEquals(expectedMaxSum, MaxSumKSizeSubarray.maxSumKSizeSubarray(arr, k));
+    }
+}
diff --git a/src/test/java/com/thealgorithms/slidingwindow/MinimumConsecutiveCardsTest.java b/src/test/java/com/thealgorithms/slidingwindow/MinimumConsecutiveCardsTest.java
new file mode 100644
index 000000000000..e00bf91ee1f9
--- /dev/null
+++ b/src/test/java/com/thealgorithms/slidingwindow/MinimumConsecutiveCardsTest.java
@@ -0,0 +1,22 @@
+package com.thealgorithms.slidingwindow;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the MinimumConsecutiveCards class.
+ *
+ * @author (https://github.com/Chiefpatwal)
+ */
+public class MinimumConsecutiveCardsTest {
+
+    @Test
+    public void testMinimumCardPickup() {
+        // Test cases for the minimumCardPickup method
+        assertEquals(2, MinimumConsecutiveCards.minimumCardPickup(new int[] {1, 2, 3, 2, 4, 1}));
+        assertEquals(-1, MinimumConsecutiveCards.minimumCardPickup(new int[] {1, 2, 3, 4, 5}));
+        assertEquals(2, MinimumConsecutiveCards.minimumCardPickup(new int[] {1, 1, 1, 1}));
+        assertEquals(2, MinimumConsecutiveCards.minimumCardPickup(new int[] {2, 2, 3, 4, 5}));
+    }
+}