Add Solution.java for 0238.Product of Array Except Self

Author: huaxu1024

solution/0238.Product of Array Except Self/README_EN.md

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+# Product of Array Except Self
+
+Given an array **nums** of n integers where _n > 1_,  return an array **output** such that **output[i]** is equal to the product of all the elements of **nums** except **nums[i]**.
+
+
+## Example 1:
+```
+ Input: [1,2,3,4]
+ Output: [24,12,8,6]
+```
+
+**Note**: Please solve it without division and in O(n).
+
+
+
+**Follow up**:
+
+Could you solve it with constant space complexity? (The output array **does not** count as extra space for the purpose of space complexity analysis.)

solution/0238.Product of Array Except Self/Solution.java

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+class Solution {
+    public int[] productExceptSelf(int[] nums) {
+        int len = nums.length;
+        int[] output = new int[len];
+        for (int i = 0, left = 1; i < len; i++) {
+            output[i] = left;
+            left *= nums[i];
+        }
+        for (int j = len - 1, right = 1; j >= 0; j--) {
+            output[j] *= right;
+            right *= nums[j];
+        }
+        return output;
+    }
+}