cs: add «238. Product of Array Except Self»

Signed-off-by: Matej Focko <mfocko@redhat.com>

cs/product-of-array-except-self.cs

@@ -0,0 +1,28 @@
+public class Solution {
+    private int Get(int[] products, int idx) {
+        if (idx < 0 || idx >= products.Length) {
+            return 1;
+        }
+        return products[idx];
+    }
+
+    public int[] ProductExceptSelf(int[] nums) {
+        var left = new int[nums.Length];
+        var right = new int[nums.Length];
+
+        for (var i = 0; i < nums.Length; ++i) {
+            left[i] = nums[i] * Get(left, i - 1);
+
+            int j = nums.Length - i - 1;
+            right[j] = nums[j] * Get(right, j + 1);
+        }
+
+        var result = new int[nums.Length];
+
+        for (var i = 0; i < nums.Length; ++i) {
+            result[i] = Get(left, i - 1) * Get(right, i + 1);
+        }
+
+        return result;
+    }
+}