Add solution of ProductOfArrayExceptSelf task

Author: andrei-punko

src/main/java/by/andd3dfx/numeric/ProductOfArrayExceptSelf.java

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+package by.andd3dfx.numeric;
+
+/**
+ * <pre>
+ * <a href="https://leetcode.com/problems/product-of-array-except-self/description/">Task description</a>
+ *
+ * Given an integer array nums, return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i].
+ *
+ * The product of any prefix or suffix of nums is guaranteed to fit in a 32-bit integer.
+ *
+ * You must write an algorithm that runs in O(n) time and without using the division operation.
+ *
+ * Example 1:
+ * Input: nums = [1,2,3,4]
+ * Output: [24,12,8,6]
+ *
+ * Example 2:
+ * Input: nums = [-1,1,0,-3,3]
+ * Output: [0,0,9,0,0]
+ * </pre>
+ */
+public class ProductOfArrayExceptSelf {
+
+    public static int[] productExceptSelf(int[] nums) {
+        var n = nums.length;
+        var left = new int[n];
+        var right = new int[n];
+
+        left[0] = nums[0];
+        for (int i = 1; i < n; i++) {
+            left[i] = left[i - 1] * nums[i];
+        }
+
+        right[n - 1] = nums[n - 1];
+        for (int i = n - 2; i >= 0; i--) {
+            right[i] = right[i + 1] * nums[i];
+        }
+
+        nums[0] = right[1];
+        nums[n - 1] = left[n - 2];
+        for (int i = 1; i < n - 1; i++) {
+            nums[i] = left[i - 1] * right[i + 1];
+        }
+        return nums;
+    }
+}

src/test/java/by/andd3dfx/numeric/ProductOfArrayExceptSelfTest.java

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+package by.andd3dfx.numeric;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class ProductOfArrayExceptSelfTest {
+
+    @Test
+    public void productExceptSelf() {
+        assertThat(ProductOfArrayExceptSelf.productExceptSelf(new int[]{0, 0, 0}))
+            .isEqualTo(new int[]{0, 0, 0});
+        assertThat(ProductOfArrayExceptSelf.productExceptSelf(new int[]{1, 1, 1, 1}))
+            .isEqualTo(new int[]{1, 1, 1, 1});
+
+        assertThat(ProductOfArrayExceptSelf.productExceptSelf(new int[]{1, 2, 3, 4}))
+            .isEqualTo(new int[]{24, 12, 8, 6});
+        assertThat(ProductOfArrayExceptSelf.productExceptSelf(new int[]{-1, 1, 0, -3, 3}))
+            .isEqualTo(new int[]{0, 0, 9, 0, 0});
+    }
+}