day 5: 21-merge-two-sorted-lists

memory shenanigans

21-merge-two-sorted-lists/driver.cpp

@@ -0,0 +1,16 @@
+#include "soln.hpp"
+
+int main()
+{
+	ListNode l1 = ListNode(2);
+	ListNode l2 = ListNode(1);
+	Solution soln;
+	ListNode *soln_ptr = soln.mergeTwoLists(&l1, &l2);
+	while (soln_ptr != nullptr)
+	{
+		cout << soln_ptr->val << " ";
+		soln_ptr = soln_ptr->next;
+	}
+	delete soln_ptr;
+	return 0;
+}

21-merge-two-sorted-lists/soln.cpp

@@ -0,0 +1,51 @@
+#include "soln.hpp"
+
+ListNode *Solution::mergeTwoLists(ListNode *list1, ListNode *list2)
+{
+	// edge cases
+	if (list1 == nullptr)
+		return list2;
+	else if (list2 == nullptr)
+		return list1;
+
+	// first node to pick to start splicing into
+	ListNode *ptr;
+	if (list1->val > list2->val)
+	{
+		ptr = list2;
+		list2 = list2->next;
+	}
+	else
+	{
+		ptr = list1;
+		list1 = list1->next;
+	}
+
+	// sort out the nodes
+	ListNode *current = ptr;
+	while (list1 && list2)
+	{
+		if (list1->val > list2->val)
+		{
+			current->next = list2;
+			list2 = list2->next;
+		}
+		else
+		{
+			current->next = list1;
+			list1 = list1->next;
+		}
+		current = current->next;
+	}
+
+	// append remaining portions
+	if (list1)
+	{
+		current->next = list1;
+	}
+	if (list2)
+	{
+		current->next = list2;
+	}
+	return ptr;
+}

21-merge-two-sorted-lists/soln.hpp

@@ -0,0 +1,20 @@
+#include <bits/stdc++.h>
+#include <iostream>
+
+using namespace std;
+
+/* Singly linked list*/
+struct ListNode
+{
+	int val;
+	ListNode *next;
+	ListNode() : val(0), next(nullptr) {}
+	ListNode(int x) : val(x), next(nullptr) {}
+	ListNode(int x, ListNode *next) : val(x), next(next) {}
+};
+
+class Solution
+{
+public:
+	ListNode *mergeTwoLists(ListNode *list1, ListNode *list2);
+};

thoughts.md

@@ -3,3 +3,4 @@
 - libraries:
   - essentials: bits/stdc++.h, iostream
   - data structures: vector
+- (q21)when working with structs, can't return locally created objects from a function, even when using new keyword...?