Add Count Nice Subarrays sliding window algorithm

Author: tarunjgupta

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

@@ -0,0 +1,39 @@
+package com.thealgorithms.slidingwindow;
+
+public class CountNiceSubarrays {
+    private CountNiceSubarrays() {
+    }
+
+    public static int countNiceSubarrays(int[] nums, int k) {
+        int n = nums.length;
+        int left = 0;
+        int oddCount = 0;
+        int result = 0;
+        int[] memo = new int[n];
+
+        for (int right = 0; right < n; right++) {
+            if ((nums[right] & 1) == 1) {
+                oddCount++;
+            }
+
+            if (oddCount > k) {
+                left += memo[left];
+                oddCount--;
+            }
+
+            if (oddCount == k) {
+                if (memo[left] == 0) {
+                    int count = 0;
+                    int temp = left;
+                    while ((nums[temp] & 1) == 0) {
+                        count++;
+                        temp++;
+                    }
+                    memo[left] = count + 1;
+                }
+                result += memo[left];
+            }
+        }
+        return result;
+    }
+}

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

@@ -0,0 +1,29 @@
+package com.thealgorithms.slidingwindow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import org.junit.jupiter.api.Test;
+
+public class CountNiceSubarraysTest {
+    @Test
+    void testExampleCase() {
+        int[] nums = {1, 1, 2, 1, 1};
+        assertEquals(2, CountNiceSubarrays.countNiceSubarrays(nums, 3));
+    }
+
+    @Test
+    void testAllEvenNumbers() {
+        int[] nums = {2, 4, 6, 8};
+        assertEquals(0, CountNiceSubarrays.countNiceSubarrays(nums, 1));
+    }
+
+    @Test
+    void testSingleOdd() {
+        int[] nums = {1};
+        assertEquals(1, CountNiceSubarrays.countNiceSubarrays(nums, 1));
+    }
+
+    @Test
+    void testMultipleChoices() {
+        int[] nums = {2, 2, 1, 2, 2, 1, 2};
+        assertEquals(9, CountNiceSubarrays.countNiceSubarrays(nums, 2));
+    }
+}