238. Product of Array Except Self (codedecks-in#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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