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308 lines (285 loc) · 8 KB
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/**
* @file
* @brief A basic unbalanced binary search tree implementation in C.
* @details The implementation has the following functionalities implemented:
* - Insertion
* - Deletion
* - Search by key value
* - Listing of node keys in order of value (from left to right)
*/
#include <stdio.h>
#include <stdlib.h>
/** Node, the basic data structure in the tree */
typedef struct node
{
struct node *left; /**< left child */
struct node *right; /**< right child */
int data; /**< data of the node */
} node;
/** The node constructor, which receives the key value input and returns a node
* pointer
* @param data data to store in a new node
* @returns new node with the provided data
* @note the node must be deleted before program terminates to avoid memory
* leaks
*/
node *newNode(int data)
{
// creates a slug
node *tmp = (node *)malloc(sizeof(node));
// initializes the slug
tmp->data = data;
tmp->left = NULL;
tmp->right = NULL;
return tmp;
}
/** Insertion procedure, which inserts the input key in a new node in the tree
* @param root pointer to parent node
* @param data value to store int he new node
* @returns pointer to parent node
*/
node *insert(node *root, int data)
{
// If the root of the subtree is null, insert key here
if (root == NULL)
{
root = newNode(data);
}
else if (data > root->data)
{
// If it isn't null and the input key is greater than the root key,
// insert in the right leaf
root->right = insert(root->right, data);
}
else if (data < root->data)
{ // If it isn't null and the input key is lower than the root key, insert
// in the left leaf
root->left = insert(root->left, data);
}
// Returns the modified tree
return root;
}
/** Utilitary procedure to find the greatest key in the left subtree
* @param root pointer to parent node
* @returns pointer to parent node
*/
node *getMax(node *root)
{
// If there's no leaf to the right, then this is the maximum key value
if (root->right != NULL)
{
return getMax(root->right);
}
return root;
}
/** Deletion procedure, which searches for the input key in the tree and removes
* it if present
* @param root pointer to parent node
* @param data value to search for int the node
* @returns pointer to parent node
*/
node *delete (node *root, int data)
{
// If the root is null, nothing to be done
if (root == NULL)
{
return root;
}
else if (data > root->data)
{ // If the input key is greater than the root's, search in the right
// subtree
root->right = delete (root->right, data);
}
else if (data < root->data)
{ // If the input key is lower than the root's, search in the left subtree
root->left = delete (root->left, data);
}
else if (data == root->data)
{
// If the input key matches the root's, check the following cases
// termination condition
if ((root->left == NULL) && (root->right == NULL))
{ // Case 1: the root has no leaves, remove the node
free(root);
return NULL;
}
else if (root->left == NULL)
{ // Case 2: the root has one leaf, make the leaf the new root and
// remove
// the old root
node *tmp = root;
root = root->right;
free(tmp);
return root;
}
else if (root->right == NULL)
{
node *tmp = root;
root = root->left;
free(tmp);
return root;
}
else
{ // Case 3: the root has 2 leaves, find the greatest key in the left
// subtree and switch with the root's
// finds the biggest node in the left branch.
node *tmp = getMax(root->left);
// sets the data of this node equal to the data of the biggest node
// (lefts)
root->data = tmp->data;
root->left = delete (root->left, tmp->data);
}
}
return root;
}
/** Search procedure, which looks for the input key in the tree and returns 1 if
* it's present or 0 if it's not in the tree
* @param root pointer to parent node
* @param data value to store int he new node
* @returns 0 if value not found in the nodes
* @returns 1 if value was found
*/
int find(node *root, int data)
{
// If the root is null, the key's not present
if (root == NULL)
{
return 0;
}
else if (data > root->data)
{
// If the input key is greater than the root's, search in the right
// subtree
return find(root->right, data);
}
else if (data < root->data)
{
// If the input key is lower than the root's, search in the left subtree
return find(root->left, data);
}
else if (data == root->data)
{
// If the input and the root key match, return 1
return 1;
}
else
{ // unknown result!!
return 0;
}
}
/** Utilitary procedure to measure the height of the binary tree
* @param root pointer to parent node
* @param data value to store int he new node
* @returns 0 if value not found in the nodes
* @returns height of nodes to get to data from parent node
*/
int height(node *root)
{
// If the root is null, this is the bottom of the tree (height 0)
if (root == NULL)
{
return 0;
}
else
{
// Get the height from both left and right subtrees to check which is
// the greatest
int right_h = height(root->right);
int left_h = height(root->left);
// The final height is the height of the greatest subtree(left or right)
// plus 1(which is the root's level)
if (right_h > left_h)
{
return (right_h + 1);
}
else
{
return (left_h + 1);
}
}
}
/** Utilitary procedure to free all nodes in a tree
* @param root pointer to parent node
*/
void purge(node *root)
{
if (root != NULL)
{
if (root->left != NULL)
{
purge(root->left);
}
if (root->right != NULL)
{
purge(root->right);
}
free(root);
root = NULL; // reset pointer
}
}
/** Traversal procedure to list the current keys in the tree in order of value
* (from the left to the right)
* @param root pointer to parent node
*/
void inOrder(node *root)
{
if (root != NULL)
{
inOrder(root->left);
printf("\t[ %d ]\t", root->data);
inOrder(root->right);
}
}
/** Main funcion */
int main()
{
// this reference don't change.
// only the tree changes.
node *root = NULL;
int opt = -1;
int data = 0;
// event-loop.
while (opt != 0)
{
printf(
"\n\n[1] Insert Node\n[2] Delete Node\n[3] Find a Node\n[4] Get "
"current Height\n[5] Print Tree in Crescent Order\n[0] Quit\n");
scanf("%d", &opt); // reads the choice of the user
// processes the choice
switch (opt)
{
case 1:
printf("Enter the new node's value:\n");
scanf("%d", &data);
root = insert(root, data);
break;
case 2:
printf("Enter the value to be removed:\n");
if (root != NULL)
{
scanf("%d", &data);
root = delete (root, data);
}
else
{
printf("Tree is already empty!\n");
}
break;
case 3:
printf("Enter the searched value:\n");
scanf("%d", &data);
find(root, data) ? printf("The value is in the tree.\n")
: printf("The value is not in the tree.\n");
break;
case 4:
printf("Current height of the tree is: %d\n", height(root));
break;
case 5:
inOrder(root);
break;
}
}
// deletes the tree from the heap.
purge(root);
return 0;
}