From b634dfae36d0ad05e7190ff63c4e4227928887f6 Mon Sep 17 00:00:00 2001
From: Kaushik Narayan R <rknarayan02@gmail.com>
Date: Sun, 15 Oct 2023 09:49:43 -0700
Subject: [PATCH] day 16: 238-product-of-array-except-self

---
 238-product-of-array-except-self/driver.cpp | 10 ++++++
 238-product-of-array-except-self/soln.cpp   | 35 +++++++++++++++++++++
 238-product-of-array-except-self/soln.hpp   |  7 +++++
 3 files changed, 52 insertions(+)
 create mode 100644 238-product-of-array-except-self/driver.cpp
 create mode 100644 238-product-of-array-except-self/soln.cpp
 create mode 100644 238-product-of-array-except-self/soln.hpp

diff --git a/238-product-of-array-except-self/driver.cpp b/238-product-of-array-except-self/driver.cpp
new file mode 100644
index 0000000..7fce4c1
--- /dev/null
+++ b/238-product-of-array-except-self/driver.cpp
@@ -0,0 +1,10 @@
+#include "soln.hpp"
+
+int main()
+{
+	vector<int> nums{1, 2, 3, 4};
+	vector<int> answer{24, 12, 8, 6};
+	Solution soln;
+	cout << "Found products correctly? " << soln.test(nums, answer) << endl;
+	return 0;
+}
\ No newline at end of file
diff --git a/238-product-of-array-except-self/soln.cpp b/238-product-of-array-except-self/soln.cpp
new file mode 100644
index 0000000..27610be
--- /dev/null
+++ b/238-product-of-array-except-self/soln.cpp
@@ -0,0 +1,35 @@
+#include "soln.hpp"
+
+vector<int> Solution::productExceptSelf(vector<int> &nums)
+{
+	int n = nums.size();
+	vector<int> pres(n);
+	vector<int> sufs(n);
+	vector<int> result(n);
+	// calculate prefixes starting from second
+	int cur = 1;
+	for (int i = 1; i < n; i++)
+	{
+		pres[i] = cur * nums[i - 1];
+		cur = pres[i];
+	}
+	// calculate suffixes starting from second last
+	cur = 1;
+	for (int j = n - 2; j >= 0; j--)
+	{
+		sufs[j] = cur * nums[j + 1];
+		cur = sufs[j];
+	}
+
+	result[0] = sufs[0];
+	result[n - 1] = pres[n - 1];
+	for (int i = 1; i < n - 1; i++)
+	{
+		result[i] = pres[i] * sufs[i];
+	}
+	return result;
+}
+
+bool Solution::test(vector<int>& nums, vector<int>& answer)	{
+	return productExceptSelf(nums) == answer;
+}
\ No newline at end of file
diff --git a/238-product-of-array-except-self/soln.hpp b/238-product-of-array-except-self/soln.hpp
new file mode 100644
index 0000000..5ac33cc
--- /dev/null
+++ b/238-product-of-array-except-self/soln.hpp
@@ -0,0 +1,7 @@
+#include <bits/stdc++.h>
+using namespace std;
+class Solution	{
+public:
+	vector<int> productExceptSelf(vector<int>& nums);
+	bool test(vector<int>& nums, vector<int>& answer);
+};
\ No newline at end of file