238. Product of Array Except Self (#228)

* Solution to problem 238

* Updated Readme

Added the row of my problem

Author: ShriAgashe

C++/238.Product_of_array_except_self

@@ -0,0 +1,54 @@
+/*
+    This code uses prefix and postfix product to evaluate answer.
+    We just need to traverse the array twice, once to the left and once to the right.
+    Then answer of ith place can be calculated using constant time.
+
+    Time Complexity : O(n)
+    Space Complexity : O(n)
+*/
+
+
+
+class Solution {
+public:
+    vector<int> productExceptSelf(vector<int>& nums) {
+        int n = nums.size(); //Variable for size of the array
+        //pre[] stores product of all numbers to the left of ith element
+        //post[] stores product of all numbers to the right of ith element
+        int pre[n],post[n]; 
+        
+        //loop to assign values to pre[]
+        int mul=1;
+        for(int i=0; i<n; i++){
+            mul*=nums[i];
+            pre[i]=mul;
+        }
+        
+        //loop to assign values to post[]
+        mul=1;
+        for(int i=n-1; i>=0; i--){
+            mul*=nums[i];
+            post[i]=mul;
+        }
+        
+        //declare a vector to return
+        vector <int> out;
+        
+        //first element of out is just going to be product of all elements except first one
+        out.push_back(post[1]);
+        
+        //value of out[i] = product of all elements except ith element
+        //which is nothing but pre[i-1]*[post[i+1]]
+        for(int i=1; i<n-1; i++){
+            int p=i-1;
+            int s=i+1;
+            out.push_back(pre[p]*post[s]);
+        }
+        
+        //last element of out is just going to be product of all elements except last one
+        out.push_back(pre[n-2]);
+        
+        //return the vector
+        return out;
+    }
+};

README.md

@@ -147,6 +147,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 1512    | [Number of Good Pairs](https://leetcode.com/problems/number-of-good-pairs/)                                                   | [Java](./Java/Number-of-Good-Pairs.java)                                                                          | O(N^2)       | O(1)          | Easy       | Array              |
 | 162     | [Find Peak element](https://leetcode.com/problems/find-peak-element/)                                                         | [javascript](https://github.com/codedecks-in/LeetCode-Solutions/blob/master/JavaScript/findPeakElement.js)                                                                     | o(Logn)      | O(1)          | Medium     | Array              |
 | 54     | [Spiral Matrix](https://leetcode.com/problems/spiral-matrix/)                                                         | [C++](./C++/Spiral-matrix.cpp)                                                                     | O(M\*N)      | O(M\*N)         | Medium     | Array              |
+| 238     | [Product of Array Except Self](https://leetcode.com/problems/product-of-array-except-self/)                                                         | [C++](./C++/238.Product_of_array_except_self)                                                                   | O(N)      | O(N)         | Medium     | Array              |
 
 
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