commit 6b23f5cdfac4ce01e635c4113d517ca1babc3c4b
Author: En Yi <randomsity1@gmail.com>
Date:   Mon Aug 26 14:23:02 2019 +0800

    First commit

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..747e990
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+*
+!.gitignore
+!*.cc
diff --git a/BST.cc b/BST.cc
new file mode 100644
index 0000000..e6bcd1c
--- /dev/null
+++ b/BST.cc
@@ -0,0 +1,112 @@
+#include <iostream>
+
+struct node{
+	int val;
+	struct node* left_child;
+	struct node* right_child;
+};
+
+node* initialise_BST_node(int val);
+void print_BST(node* root);
+void delete_BST(node* root);
+void insert(node* root, int val);
+void delete_node(node* root, int val, node* prev_node);
+
+int main(){
+	node* root = initialise_BST_node(5);
+	insert(root, 3);
+	insert(root, 10);
+	insert(root, 4);
+	insert(root, 8);
+	insert(root, 14);
+	insert(root, 1);
+	print_BST(root);
+	std::cout << std::endl;
+	delete_node(root, 8, NULL);
+	print_BST(root);
+	std::cout << std::endl;
+	delete_BST(root);
+}
+
+node* initialise_BST_node(int val){
+	node* root = new node();
+	root->val = val;
+	root->left_child = NULL;
+	root->right_child = NULL;
+	return root;	
+}
+
+void print_BST(node* root){
+	if (root->left_child != NULL)
+		print_BST(root->left_child);
+	std::cout << root->val << " ";
+	if (root->right_child != NULL)
+		print_BST(root->right_child);
+}
+
+void delete_BST(node* root){
+	if (root->left_child != NULL)
+		delete_BST(root->left_child);
+	if (root->right_child != NULL)
+		delete_BST(root->right_child);
+	delete root;
+}
+
+void insert(node* root, int val){
+	if (val == root->val)
+		return;
+	
+	if (val < root->val){
+		if (root->left_child != NULL)
+			insert(root->left_child, val);
+		else{
+			node* new_node = initialise_BST_node(val);
+			root->left_child = new_node;
+		}
+	}else{
+		if (root->right_child != NULL)
+			insert(root->right_child, val);
+		else{
+			node* new_node = initialise_BST_node(val);
+			root->right_child = new_node;
+		}
+	}
+}
+
+void delete_node(node* root, int val, node* prev_node){
+	if (root->left_child != NULL && val < root->val)
+		delete_node(root->left_child, val, root);
+	if (root->right_child != NULL && val > root->val)
+		delete_node(root->right_child, val, root);
+
+	if (root->val == val){
+		node* replacing_node = NULL;
+		if (root->left_child != NULL && root->left_child != NULL){
+			replacing_node = root->right_child;
+			while (replacing_node->left_child != NULL){
+				replacing_node = replacing_node->left_child;
+			}			
+		}
+		else if (root->left_child != NULL)
+			replacing_node = root->left_child;	
+		else if	(root->right_child != NULL)
+			replacing_node = root->right_child;
+
+		if (replacing_node != NULL){
+			replacing_node->left_child = root->left_child;
+			replacing_node->right_child = root->right_child;
+		}
+
+		if (prev_node != NULL){
+			if (prev_node->left_child == root)
+				prev_node->left_child = replacing_node;
+			if (prev_node->right_child == root)
+				prev_node->right_child = replacing_node;				
+		}
+		delete root;
+	}
+}
+
+	
+	
+
diff --git a/linked_list.cc b/linked_list.cc
new file mode 100644
index 0000000..5731450
--- /dev/null
+++ b/linked_list.cc
@@ -0,0 +1,99 @@
+#include <iostream>
+
+struct node{
+	int val;
+	node *next;
+};
+
+node* initiate_linked_list(int val);
+void print_linked_list(node* head);
+void push(node** head, int val);
+int pop(node* head);
+int search(node* head, int val);
+void delete_linked_list(node* head);
+node* recursive_reverse(node* head);
+
+int main(){
+	node *head = initiate_linked_list(1);
+	print_linked_list(head);
+	push(&head, 5);
+	push(&head, 2);
+	push(&head, 7);
+	push(&head, 9);
+	print_linked_list(head);
+	head = recursive_reverse(head);
+	print_linked_list(head);
+	std::cout << search(head, 7) << std::endl;
+	std::cout << search(head, 10) << std::endl;
+	pop(head);
+	print_linked_list(head);
+	delete_linked_list(head);
+}
+
+node* initiate_linked_list(int val){
+	node *head = new node();
+	head->val = val;
+	return head;
+}
+
+void print_linked_list(node* head){
+	node *current_node = head;
+	while (current_node != NULL){
+		std::cout << current_node->val << " ";
+		current_node = current_node->next;
+	}
+	std::cout << std::endl;
+}
+
+void push(node** head, int val){
+	node *new_node = new node();
+	new_node->val = val;
+	new_node->next = *head;
+	*head = new_node;
+}
+
+int pop(node* head){
+	node *current_node = head;
+	while (current_node->next->next != NULL){
+		current_node = current_node->next;
+	}
+	int val = current_node->next->val;
+	delete current_node->next;
+	current_node->next = NULL;
+	return val;
+}
+
+int search(node* head, int val){
+	node *current_node = head;
+	int index = 0;
+	while (current_node != NULL){
+		if (current_node->val == val)
+			return index;
+		current_node = current_node->next;
+		++index;
+	}
+	return -1;
+}
+
+void delete_linked_list(node* head){
+	node *current_node = head;
+	node *next_node;
+	while (current_node != NULL){
+		next_node = current_node->next;
+		delete current_node;
+		current_node = next_node;
+	}
+}
+
+node* recursive_reverse(node* head){
+	node* current_node = head; // For clarity
+	if (current_node->next != NULL){
+		node* new_head = recursive_reverse(current_node->next);
+		current_node->next->next = current_node;
+		current_node->next = NULL;
+		return new_head;
+	}else{
+		return current_node;
+	}
+	
+}
diff --git a/mergesort.cc b/mergesort.cc
new file mode 100644
index 0000000..ba3f072
--- /dev/null
+++ b/mergesort.cc
@@ -0,0 +1,156 @@
+/** This is the code for sorting linked list using mergesort
+as a practice using C++. Also for practice using Vim :p
+Feel free to modify.
+**/
+
+#include <iostream>
+#include <stdlib.h>
+#include <time.h>
+
+struct node{
+	int val;
+	node *next;
+};
+
+int generate_random_number(int upper_bound);
+node* initiate_linked_list(int val);
+void print_linked_list(node* head);
+void push(node** head, int val);
+void delete_linked_list(node* head);
+node* merge_sort(node* head);
+
+int main(int argc, char** argv){
+	int n;
+	int upper_bound;
+	// Input checking. Could've used a loop, but I'm not bothered :p
+	if(argc == 3){
+		char* endp;
+		char* endp2;
+		int val = strtol(argv[1], &endp, 10);
+		int val2 = strtol(argv[2], &endp2, 10);
+		if (!*endp && !*endp2){
+			n = val;
+			upper_bound = val2;
+		}else{
+			std::cout << "Usage: ./mergesort val1 val2"<< std::endl;
+			std::cout << "val1 is the length of the array, int" << std::endl;
+			std::cout << "val2 is the upper bound of the random number (exclusive), int" << std::endl;
+			return 1;
+		}
+	}else{
+		std::cout << "Usage: ./mergesort val1 val2"<< std::endl;
+		std::cout << "val1 is the length of the array, int" << std::endl;
+		std::cout << "val2 is the upper bound of the random number (exclusive), int" << std::endl;
+		return 1;
+	}
+
+	srand (time(NULL));
+	node* head = initiate_linked_list(generate_random_number(upper_bound));
+	--n;
+
+	for(int i=0;i<n;++i){
+		push(&head, generate_random_number(upper_bound));
+	}
+
+	std::cout << "Before: "<<std::endl;
+	print_linked_list(head);
+	head = merge_sort(head);
+
+	std::cout << "After: "<<std::endl;
+	print_linked_list(head);
+	delete_linked_list(head);
+}
+
+
+node* merge_sort(node* head){
+	// Return if list is only one node
+	if (head->next == NULL)
+		return head;
+
+	// Get to the half way of the list
+	node *p1 = head, *p2 = head;
+	while(p1->next != NULL && p1->next->next != NULL){
+		p1 = p1->next->next;
+		p2 = p2->next;
+	}
+
+	// Break into two lists
+	p1 = p2->next;
+	p2->next = NULL; 
+	
+	// Sort the two halves, recursively
+	p1 = merge_sort(p1);
+	//print_linked_list(p1);
+	p2 = merge_sort(head);
+	//print_linked_list(p2);
+	
+	node *newHead = NULL;
+	node *current;
+	node **smaller; // Address of pointer of smaller value
+	// If either still have an element
+	while(p1 != NULL || p2 != NULL){
+		// Get whichever address of pointer to smaller value
+		// Get the other if one is null
+		if(p1 == NULL)
+			smaller = &p2;
+		else if(p2 == NULL)
+			smaller = &p1;
+		else{
+			if(p1->val < p2->val)
+				smaller = &p1;
+			else
+				smaller = &p2;
+		}
+
+		// If newHead is null (first element), make one
+		// Otherwise append the current node
+		// Require dereferencing the smaller variable
+		if (newHead == NULL){
+			newHead = *smaller;
+		}else{
+			current->next = *smaller;
+		}
+		// Make the current pointer at the appended node
+		current = *smaller;
+		// Shift the pointer of the smaller value to the next
+		*smaller = (*smaller)->next;			
+	}
+	return newHead;
+}
+
+int generate_random_number(int upper_bound){
+	return rand() % upper_bound;
+}
+
+node* initiate_linked_list(int val){
+	node *head = new node();
+	head->val = val;
+	return head;
+}
+
+void print_linked_list(node* head){
+	node *current_node = head;
+	while (current_node != NULL){
+		std::cout << current_node->val << " ";
+		current_node = current_node->next;
+	}
+	std::cout << std::endl;
+}
+
+void push(node** head, int val){
+	node *new_node = new node();
+	new_node->val = val;
+	new_node->next = *head;
+	*head = new_node;
+}
+
+void delete_linked_list(node* head){
+	node *current_node = head;
+	node *next_node;
+	while (current_node != NULL){
+		next_node = current_node->next;
+		delete current_node;
+		current_node = next_node;
+	}
+}
+