Merge pull request #545 from amitnayakblr/master

Threaded binary tree

data_structures/binary_trees/threaded_binary_trees.c

@@ -0,0 +1,247 @@
+/**
+ * @file
+ * \brief This file is a simple implementation of a Threaded Binary Tree
+ *
+ * Threaded Binary Tree is a binary tree variant in which all left child
+ * pointers that are NULL (in Linked list representation) point to its
+ * in-order predecessor, and all right child pointers that are NULL
+ * (in Linked list representation) point to its in-order successor.
+ * It has the following functionalities:
+ * - Insertion
+ * - Search
+ * - Deletion
+ * - Listing of node keys inorder,preorder,postorder
+ *
+ * -see binary_search_tree.c
+ *
+ * \author [Amitha Nayak](https://github.com/amitnayakblr)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+/**
+ * Node, the basic data structure of the tree
+ **/
+typedef struct Node {
+  int data;           /**< stores the number */
+  struct Node *llink; /**< link to left child */
+  struct Node *rlink; /**< link to right child */
+} node;
+
+/**
+ * creates a new node
+ * param[in] data value to be inserted
+ * \returns a pointer to the new node
+ **/
+node *create_node(int data) {
+  node *ptr = (node *)malloc(sizeof(node));
+  ptr->rlink = ptr->llink = NULL;
+  ptr->data = data;
+  return ptr;
+}
+
+/**
+ * inserts a node into the tree
+ * param[in,out] root pointer to node pointer to the topmost node of the tree
+ * param[in] data value to be inserted into the tree
+ */
+void insert_bt(node **root, int data) {
+  node *new_node = create_node(data);
+  node *temp; // to be deleted
+  node *prev; // keeps track of the parent of the element deleted
+  if (*root == NULL) {
+    *root = new_node;
+  } else {
+    temp = *root;
+    prev = NULL;
+    while (temp != NULL) {
+      if (new_node->data > temp->data) {
+        prev = temp;
+        temp = temp->rlink;
+      } else if (new_node->data < temp->data) {
+        prev = temp;
+        temp = temp->llink;
+      } else {
+        return;
+      }
+    }
+
+    if (new_node->data > prev->data) {
+      prev->rlink = new_node;
+    } else {
+      prev->llink = new_node;
+    }
+  }
+}
+
+/**
+ * searches for the element
+ * \param[in] root node pointer to the topmost node of the tree
+ * \param[in] ele value searched for
+ */
+void search(node *root, int ele) {
+  node *temp = root;
+  while (temp != NULL) {
+    if (temp->data == ele) {
+      break;
+    } else if (ele > temp->data) {
+      temp = temp->rlink;
+    } else {
+      temp = temp->llink;
+    }
+  }
+
+  if (temp == NULL) {
+    printf("%s\n", "Element not found.");
+  } else
+    printf("%s\n", "Element found.");
+}
+
+/**
+ * performs inorder traversal
+ * param[in] curr node pointer to the topmost node of the tree
+ */
+void inorder_display(node *curr) {
+  if (curr != NULL) {
+    inorder_display(curr->llink);
+    printf("%d\t", curr->data);
+    inorder_display(curr->rlink);
+  }
+}
+
+/**
+ * performs postorder traversal
+ * param[in] curr node pointer to the topmost node of the tree
+ */
+void postorder_display(node *curr) {
+  if (curr != NULL) {
+    postorder_display(curr->llink);
+    postorder_display(curr->rlink);
+    printf("%d\t", curr->data);
+  }
+}
+
+/**
+ * performs preorder traversal
+ * param[in] curr node pointer to the topmost node of the tree
+ */
+void preorder_display(node *curr) {
+  if (curr != NULL) {
+    printf("%d\t", curr->data);
+    preorder_display(curr->llink);
+    preorder_display(curr->rlink);
+  }
+}
+
+/**
+ * deletion of a node from the tree
+ * if the node isn't present in the tree, it takes no action.
+ * param[in,out] root pointer to node pointer to the topmost node of the tree
+ * param[in] ele value to be deleted from the tree
+ */
+void delete_bt(node **root, int ele) {
+  node *temp;
+  node *prev;
+  if (*root == NULL)
+    return;
+  else {
+    temp = *root;
+    prev = NULL;
+    // search
+    while (temp != NULL) {
+      if (temp->data == ele) {
+        break;
+      } else if (ele > temp->data) {
+        prev = temp;
+        temp = temp->rlink;
+      } else {
+        prev = temp;
+        temp = temp->llink;
+      }
+    }
+  }
+
+  if (temp == NULL)
+    return;
+  else {
+    node *replacement; // deleted node's replacement
+    node *t;
+    if (temp->llink == NULL && temp->rlink == NULL) {
+      replacement = NULL;
+    } else if (temp->llink == NULL && temp->rlink != NULL) {
+      replacement = temp->rlink;
+    } else if (temp->llink != NULL && temp->rlink == NULL) {
+      replacement = temp->llink;
+    } else {
+      replacement = temp->rlink; // replaced with inorder successor
+      t = replacement;
+      while (t->llink != NULL) {
+        t = t->llink;
+      }
+      t->llink = temp->llink; // leftmost node of the replacement is linked to
+                              // the left child of the deleted node
+    }
+
+    if (temp == *root) {
+      free(*root);
+      *root = replacement;
+    } else if (prev->llink == temp) {
+      free(prev->llink);
+      prev->llink = replacement;
+    } else if (prev->rlink == temp) {
+      free(prev->rlink);
+      prev->rlink = replacement;
+    }
+  }
+}
+
+/**
+ * main function
+ */
+int main() {
+  printf("BINARY THREADED TREE: \n");
+  node *root = NULL;
+  int choice, n;
+  do {
+    printf("%s\n", "1. Insert into BT");
+    printf("%s\n", "2. Print BT - inorder");
+    printf("%s\n", "3. Print BT - preorder");
+    printf("%s\n", "4. print BT - postorder");
+    printf("%s\n", "5. delete from BT");
+    printf("%s\n", "6. search in BT");
+    printf("%s\n", "Type 0 to exit");
+    scanf("%d", &choice);
+
+    switch (choice) {
+    case 1:
+      printf("%s\n", "Enter a no:");
+      scanf("%d", &n);
+      insert_bt(&root, n);
+      break;
+    case 2:
+      inorder_display(root);
+      printf("\n");
+      break;
+    case 3:
+      preorder_display(root);
+      printf("\n");
+      break;
+    case 4:
+      postorder_display(root);
+      printf("\n");
+      break;
+    case 5:
+      printf("%s\n", "Enter a no:");
+      scanf("%d", &n);
+      delete_bt(&root, n);
+      break;
+    case 6:
+      printf("%s\n", "Enter a no:");
+      scanf("%d", &n);
+      search(root, n);
+      break;
+    }
+  } while (choice != 0);
+  return 0;
+}