[LEET-238] add 238

Author: fishercoder1534

leetcode-algorithms/README.md

@@ -166,7 +166,7 @@
 |243|[Shortest Word Distance](https://leetcode.com/problems/shortest-word-distance/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/ShortestWordDistance.java) | O(n) | O(1) | 
 |240|[Search a 2D Matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/Searcha2DMatrixII.java)| O(log(m*n))|O(1) | Medium| Binary Search
 |239|[Sliding Window Maximum](https://leetcode.com/problems/sliding-window-maximum/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/SlidingWindowMaximum.java)| O(nlogn)|O(k) | Hard| Heap
-|238|[Product of Array Except Self](https://leetcode.com/problems/product-of-array-except-self/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/ProductOfArrayExceptItself.java)| O(?)|O(?) | Medium|
+|238|[Product of Array Except Self](https://leetcode.com/problems/product-of-array-except-self/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/ProductofArrayExceptSelf.java)| O(n)|O(1) | Medium| Array
 |237|[Delete Node in a Linked List](https://leetcode.com/problems/delete-node-in-a-linked-list/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/DeleteNodeInALinkedList.java)| O(1)|O(1) | Easy| LinkedList
 |235|[Lowest Common Ancestor of a Binary Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/LowestCommonAncestorOfABinaryTree.java)| O(h)|O(1) | Medium| DFS
 |235|[Lowest Common Ancestor of a Binary Search Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/LowestCommonAncestorOfABinarySearchTree.java)| O(h)|O(1) | Easy| DFS

leetcode-algorithms/src/main/java/com/stevesun/solutions/ProductOfArrayExceptItself.java

@@ -0,0 +1,29 @@
+package com.stevesun.solutions;
+
+/**
+ * Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].
+
+ Solve it without division and in O(n).
+
+ For example, given [1,2,3,4], return [24,12,8,6].
+
+ Follow up:
+ Could you solve it with constant space complexity? (Note: The output array does not count as extra space for the purpose of space complexity analysis.)
+ */
+public class ProductofArrayExceptSelf {
+
+    public int[] productExceptSelf(int[] nums) {
+        int n = nums.length;
+        int[] result = new int[n];
+        result[0] = 1;
+        for (int i = 1; i < n; i++) {
+            result[i] = result[i-1]*nums[i-1];
+        }
+        int right = 1;
+        for (int i = n-1; i >= 0; i--) {
+            result[i] *= right;
+            right *= nums[i];
+        }
+        return result;
+    }
+}

leetcode-algorithms/src/main/java/com/stevesun/solutions/ProductofArrayExceptSelf.java

@@ -0,0 +1,42 @@
+package com.stevesun;
+
+import com.stevesun.solutions.ProductofArrayExceptSelf;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertArrayEquals;
+
+public class ProductofArrayExceptSelfTest {
+    private static ProductofArrayExceptSelf test;
+    private static int[] expected;
+    private static int[] actual;
+    private static int[] nums;
+
+    @BeforeClass
+    public static void setup(){
+        test = new ProductofArrayExceptSelf();
+    }
+
+    @Before
+    public void setupForEachTest(){
+        expected = new int[]{};
+        actual = new int[]{};
+    }
+
+    @Test
+    public void test1(){
+        nums = new int[]{0, 0};
+        expected = new int[]{0, 0};
+        actual = test.productExceptSelf(nums);
+        assertArrayEquals(expected, actual);
+    }
+
+    @Test
+    public void test2(){
+        nums = new int[]{1, 0};
+        expected = new int[]{0, 1};
+        actual = test.productExceptSelf(nums);
+        assertArrayEquals(expected, actual);
+    }
+}