Add Subarray Product Less Than K Problem (#18)

xtenzQ · Jul 6, 2024 · d5aea5d · d5aea5d
1 parent c201cea
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diff --git a/algorithms-and-data-structures/src/main/java/com/xtenzq/arrays/SlidingWindow.java b/algorithms-and-data-structures/src/main/java/com/xtenzq/arrays/SlidingWindow.java
@@ -50,4 +50,35 @@ public static int findLongestSubstringAfterOneFlip(String s) {
         }
         return answer;
     }
+
+    /**
+     * Returns the number of subarrays where the product of all the elements in the subarray
+     * is strictly less than {@code k}.
+     *
+     * @param nums the array of positive integers
+     * @param k the integer threshold
+     * @return the number of subarrays with product less than {@code k}
+     * @implNote This method runs in {@code O(n)} time complexity and {@code O(1)} space complexity,
+     * where {@code n} is the length of {@code nums}.
+     * @see <a href="https://leetcode.com/problems/subarray-product-less-than-k/">713. Subarray Product Less Than K</a>
+     */
+    public static int numSubarrayProductLessThanK(int[] nums, int k) {
+        if (k <= 1) {
+            return 0;
+        }
+
+        int left = 0, count = 1, answer = 0;
+
+        for (int right = 0; right < nums.length; right++) {
+            count *= nums[right];
+            while (count >= k) {
+                count /= nums[left];
+                left++;
+            }
+
+            answer += right - left + 1;
+        }
+
+        return answer;
+    }
 }
diff --git a/algorithms-and-data-structures/src/test/java/com/xtenzq/arrays/SlidingWindowTest.java b/algorithms-and-data-structures/src/test/java/com/xtenzq/arrays/SlidingWindowTest.java
@@ -4,6 +4,7 @@
 
 import static com.xtenzq.arrays.SlidingWindow.findLongestSubstringAfterOneFlip;
 import static com.xtenzq.arrays.SlidingWindow.findLongestSubArraySumLessOrEqualK;
+import static com.xtenzq.arrays.SlidingWindow.numSubarrayProductLessThanK;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class SlidingWindowTest {
@@ -103,4 +104,39 @@ void testFindLongestSubstringAfterOneFlip_ComplexPattern() {
         String s = "100110111001111";
         assertEquals(6, findLongestSubstringAfterOneFlip(s));
     }
+
+    @Test
+    void testNumSubarrayProductLessThanK_SubarraysWithProductLessThan100() {
+        int[] nums = {10, 5, 2, 6};
+        int k = 100;
+        assertEquals(8, numSubarrayProductLessThanK(nums, k));
+    }
+
+    @Test
+    void testNumSubarrayProductLessThanK_SubarraysWithProductLessThan0() {
+        int[] nums = {1, 2, 3};
+        int k = 0;
+        assertEquals(0, numSubarrayProductLessThanK(nums, k));
+    }
+
+    @Test
+    void testNumSubarrayProductLessThanK_SubarraysWithProductLessThan1() {
+        int[] nums = {1, 2, 3};
+        int k = 1;
+        assertEquals(0, numSubarrayProductLessThanK(nums, k));
+    }
+
+    @Test
+    void testNumSubarrayProductLessThanK_SubarraysWithProductLessThan10() {
+        int[] nums = {1, 2, 3};
+        int k = 10;
+        assertEquals(6, numSubarrayProductLessThanK(nums, k));
+    }
+
+    @Test
+    void testNumSubarrayProductLessThanK_EmptyArray() {
+        int[] nums = {};
+        int k = 100;
+        assertEquals(0, numSubarrayProductLessThanK(nums, k));
+    }
 }