From 4d2146759d705c49966968bbc5273ef3767bc914 Mon Sep 17 00:00:00 2001
From: Jidong Xiao <xiaoj8@rpi.edu>
Date: Mon, 9 Oct 2023 12:22:32 -0400
Subject: [PATCH] adding checkpoint 3 code

---
 labs/07_list_implementation/README.md       |   9 +-
 labs/07_list_implementation/checkpoint3.cpp | 107 ++++++++++++++++++++
 2 files changed, 112 insertions(+), 4 deletions(-)
 create mode 100644 labs/07_list_implementation/checkpoint3.cpp

diff --git a/labs/07_list_implementation/README.md b/labs/07_list_implementation/README.md
index ab6e5cd..79a3238 100644
--- a/labs/07_list_implementation/README.md
+++ b/labs/07_list_implementation/README.md
@@ -44,11 +44,12 @@ Debugging a Merge Sort program. We expect our program [checkpoint3.cpp](checkpoi
 ```console
 $ g++ checkpoint3.cpp
 $ ./a.out
-Test Case 1: Original Array: 5 2 9 1 5 6
-Sorted Array: 1 2 5 5 6 9
+Test Case 1: Original Vector: 5 2 9 1 5 6
+Sorted Vector: 1 2 5 5 6 9
+
+Test Case 2: Original Vector: 3 8 2 7 4
+Sorted Vector: 2 3 4 7 8
 
-Test Case 2: Original Array: 3 8 2 7 4
-Sorted Array: 2 3 4 7 8
 ```
 
 But this program currently does not behave as expected. Please use a debugger to troubleshoot this program, find the problems and fix them.
diff --git a/labs/07_list_implementation/checkpoint3.cpp b/labs/07_list_implementation/checkpoint3.cpp
new file mode 100644
index 0000000..29177e4
--- /dev/null
+++ b/labs/07_list_implementation/checkpoint3.cpp
@@ -0,0 +1,107 @@
+#include <iostream>
+#include <vector>
+
+// prototype of the sorting function
+std::vector<int> sortVector(std::vector<int>& nums);
+
+// function to print the elements of a vector
+void printVector(const std::vector<int>& nums) {
+	for (int num : nums) {
+		std::cout << num << " ";
+	}
+	std::cout << std::endl;
+}
+
+int main() {
+	// test case 1
+	std::vector<int> test1 = {5, 2, 9, 1, 5, 6};
+	std::vector<int> result1 = sortVector(test1);
+	std::cout << "Test Case 1: Original Vector: ";
+	printVector(test1);
+	std::cout << "Sorted Vector: ";
+	printVector(result1);
+	std::cout << std::endl;
+
+	// test case 2
+	std::vector<int> test2 = {3, 8, 2, 7, 4};
+	std::vector<int> result2 = sortVector(test2);
+	std::cout << "Test Case 2: Original Vector: ";
+	printVector(test2);
+	std::cout << "Sorted Vector: ";
+	printVector(result2);
+	std::cout << std::endl;
+
+	return 0;
+}
+
+// merge two vectors which are already sorted
+std::vector<int>& mergeVectors(std::vector<int>& v1, std::vector<int>& v2){
+	int size1 = v1.size();
+	int size2 = v2.size();
+	std::vector<int> v(size1+size2, 0);
+	int index1 = 0;
+	int index2 = 0;
+	int index = 0;
+	// traverse v1 and v2 at the same time
+	while(index1<size1 && index2<size2){
+		// whoever is smaller goes to v
+		if(v1[index1]<v2[index2]){
+			v[index] = v1[index1];
+			index1 = index1 + 1;
+		}else{
+			v[index] = v2[index2];
+			index2 = index2 + 1;
+		}
+		index = index + 1;
+	}
+
+	// if v1 is done, let's now deal with v2 left overs
+	if(index1>=size1){
+		while(index2<size2){
+			v[index] = v2[index2];
+			index++;
+			index2++;
+		}
+	}else{
+		// else means v2 is done. let's now deal with v1 left overs
+		while(index1<size1){
+			v[index] = v1[index1];
+			index++;
+			index1++;
+		}
+	}
+	return v;
+}
+
+// sort a vecotr of integers
+std::vector<int> sortVector(std::vector<int>& nums) {
+	int size = nums.size();
+	// base case
+	if(size==1){
+		return nums;
+	}
+	// general case
+	// split the vector into two halves.
+	int mid = size/2;
+	
+	// nums1 to store the first half, and nums2 to store the second half.
+	std::vector<int> nums1;
+	std::vector<int> nums2;
+	
+	// copy the first half
+	for(int i=0;i<mid;i++){
+		nums1[i]=nums[i];
+	}
+	// copy the second half
+	for(int i=mid;i<size;i++){
+		nums2[i]=nums[i];
+	}
+
+	// make the recursive calls
+	nums1 = sortVector(nums1);
+	nums2 = sortVector(nums2);
+	
+	// now that the two vectors are already sorted, let's merge them
+	return mergeVectors(nums1, nums2);
+}
+