C Program to Print Level of a Given Node in Binary Tree

• Write a C program to print level of a node in binary tree.
• Recursive function in C to find level of a given node in binary tree.

Given a binary tree and a node N, we have to print the level of node N in binary tree. To print the level of a node N, first of all we have to search it in binary tree. Here, we can use In Order, pre Order or post Order traversal to search node N in binary tree. We will also keep track of level of current node while traversing.

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Algorithm to find level of a given node in binary tree

• Traverse given binary tree using pre order traversal by keeping track of levels of nodes.
• Let node be the pointer to any node at level L.
• If node is equal to NULL, return.
• If node is equal to N, then print the level of node(L) on screen else continue traversal of sub trees at level L+1.

Time Complexity : O(n), we are traversing binary tree only once.

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C program to print level of a given node of binary tree

 #include <stdio.h>

struct node {
    int data;
    struct node *left;
    struct node *right;
};

struct node* getNewNode(int data) {
  /* dynamically allocate memory for a new node */ 
  struct node* newNode = (struct node*)malloc(sizeof(struct node));
 
  /* populate data in new Node */
  newNode->data = data;
  newNode->left = NULL;
  newNode->right = NULL;
  
  return newNode;
}

/*
This function returns below tree
            1
           / \
         2    3
        / \  / \
       4  5 6  7
      / \       \
     8  9       10
*/
struct node* generateBTree(){
    // Root Node
    struct node* root =  getNewNode(1);
 
    root->left = getNewNode(2);
    root->right = getNewNode(3);
 
    root->left->left = getNewNode(4);
    root->left->right = getNewNode(5);
    root->right->left = getNewNode(6);
    root->right->right = getNewNode(7);
 
    root->left->left->left = getNewNode(8);
    root->left->left->right = getNewNode(9);
    
    root->right->right->right = getNewNode(10);
    
    return root;
}

/* 
   Prints level of all nodes. It does pre Order 
   traversal and keeps track of the current level and prints it.
*/
void printLevelOfNode(struct node* root, int currentLevel, int num) {
  
    if(root == NULL) {
        return;   
    }
 
 if(root->data == num) {
        printf("Level of %d is %d \n", num, currentLevel);
 }
             
    printLevelOfNode(root->left, currentLevel+1, num);
    printLevelOfNode(root->right, currentLevel+1, num);
}

int main() {
    struct node *root = generateBTree();    
    
    /*Printing level of nodes */
    printLevelOfNode(root, 0, 1);
    printLevelOfNode(root, 0, 5);
    printLevelOfNode(root, 0, 7);
    printLevelOfNode(root, 0, 9);
    
    getchar();
    return 0; 
}

Output

Level of 1 is 0
Level of 5 is 2
Level of 7 is 2
Level of 9 is 3