added new algo

Author: Chiefpatwal

src/main/java/com/thealgorithms/slidingwindow/SubarraysWithKDifferentIntegers.java

@@ -0,0 +1,58 @@
+package com.thealgorithms.slidingwindow;
+
+/**
+ * The Subarrays with K Different Integers algorithm counts the number of subarrays
+ * that contain exactly k distinct integers.
+ *
+ * <p>
+ * Worst-case performance O(n)
+ * Best-case performance O(n)
+ * Average performance O(n)
+ * Worst-case space complexity O(k)
+ *
+ * @author https://github.com/Chiefpatwal
+ */
+public final class SubarraysWithKDifferentIntegers {
+
+    // Prevent instantiation
+    private SubarraysWithKDifferentIntegers() {
+    }
+
+    /**
+     * This method counts the number of subarrays with exactly k different integers.
+     *
+     * @param arr is the input array
+     * @param k   is the number of distinct integers
+     * @return the count of subarrays with exactly k distinct integers
+     */
+    public static int subarraysWithKDistinct(int[] arr, int k) {
+        return atMostKDistinct(arr, k) - atMostKDistinct(arr, k - 1);
+    }
+
+    // Helper method to count subarrays with at most k distinct integers
+    private static int atMostKDistinct(int[] arr, int k) {
+        if (k <= 0) return 0;
+
+        int count = 0; // To store the count of valid subarrays
+        int left = 0; // Left index of the sliding window
+        int[] frequency = new int[arr.length + 1]; // Frequency array to count distinct integers
+
+        for (int right = 0; right < arr.length; right++) {
+            if (frequency[arr[right]] == 0) {
+                k--; // New distinct integer added
+            }
+            frequency[arr[right]]++; // Increment the frequency of the current element
+
+            while (k < 0) { // More than k distinct integers
+                frequency[arr[left]]--; // Remove the leftmost element from the window
+                if (frequency[arr[left]] == 0) {
+                    k++; // Distinct integer count reduced
+                }
+                left++; // Move the left index to the right
+            }
+            count += right - left + 1; // Count the number of valid subarrays ending at 'right'
+        }
+
+        return count; // Return the total count
+    }
+}

src/test/java/com/thealgorithms/slidingwindow/SubarraysWithKDifferentIntegersTest.java

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+package com.thealgorithms.slidingwindow;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test cases for SubarraysWithKDifferentIntegers algorithm.
+ *
+ * <p>
+ * This class provides test cases to verify the correctness of the subarraysWithKDistinct
+ * method.
+ *
+ * @author https://github.com/Chiefpatwal
+ */
+public class SubarraysWithKDifferentIntegersTest {
+
+    @Test
+    public void testEdgeCases() {
+        // Test with an empty array
+        assertEquals(0, SubarraysWithKDifferentIntegers.subarraysWithKDistinct(new int[] {}, 1));
+
+        // Test with k greater than the number of distinct elements
+        assertEquals(0, SubarraysWithKDifferentIntegers.subarraysWithKDistinct(new int[] {1, 2, 3}, 5));
+
+        // Test with k = 0
+        assertEquals(0, SubarraysWithKDifferentIntegers.subarraysWithKDistinct(new int[] {1, 2, 3}, 0));
+
+        // Test with single element arrays
+        assertEquals(1, SubarraysWithKDifferentIntegers.subarraysWithKDistinct(new int[] {1}, 1));
+        assertEquals(0, SubarraysWithKDifferentIntegers.subarraysWithKDistinct(new int[] {1}, 2));
+
+        // Test case where all elements are the same
+        assertEquals(6, SubarraysWithKDifferentIntegers.subarraysWithKDistinct(new int[] {2, 2, 2}, 1)); // Corrected expected value
+        assertEquals(0, SubarraysWithKDifferentIntegers.subarraysWithKDistinct(new int[] {2, 2, 2}, 2)); // Not enough distinct elements
+    }
+}