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Print root to leaf paths without using recursion in C++ Programming.
Given the binary tree the program must find out the multiple paths from the root to a leaf which means all the paths should be printed but the challenge is to without using recursion.
We will traverse the tree iteratively as the constraint is to do it without recursion. So to achieve this we can use an STL map that will store the root element and whenever the leaf node is identified through level order traversal it will print the path from root to leaf as there is a map pointer which is pointing to a root node.
In the above tree, there are multiple paths which can be generated for reaching from root to leaf −
10 -> 3 -> 140 10 -> 3 -> 162 10 -> 211 -> 100 10 -> 211 -> 146
Hence, the program must print all the given paths as an output of the given binary tree.
Algorithm
START Step 1 -> create a structure of a node as struct Node struct node *left, *right int data End Step 2 -> function to create a node node* newnode(int data) node->data = data node->left = node->right = NULL; return (node) Step 3 -> create function to calculate the path void calculatePath(Node* curr, map<Node*, Node*> first) create STL stack<Node*> stk Loop While (curr) stk.push(curr) curr = first[curr] End Loop While !stk.empty() curr = stk.top() stk.pop() print curr->data End Step 4 -> create function to find the leaf nodes void leaf(Node* root) IF root = NULL Return End Create STL stack<Node*> stc stc.push(root) Create STL map<Node*, Node*> prnt prnt[root] = NULL Loop while !stc.empty() Node* curr = stc.top() stc.pop() IF!(curr->left) && !(curr->right) calculatePath(curr, prnt) End IF curr->right prnt[curr->right] = curr stc.push(curr->right) End IF curr->left prnt[curr->left] = curr stc.push(curr->left) End End STOP
Example
#include <bits/stdc++.h>
using namespace std;
//structure of a node
struct Node{
int data;
struct Node *left, *right;
};
//function to create a new node
Node* newNode(int data){
Node* node = new Node;
node->data = data;
node->left = node->right = NULL;
return node;
}
//this function will calculate the path
void calculatePath(Node* curr, map<Node*, Node*> first){
stack<Node*> stk;
while (curr){
stk.push(curr);
curr = first[curr];
}
while (!stk.empty()){
curr = stk.top();
stk.pop();
cout << curr->data << " ";
}
cout << endl;
}
//this function will lead to the leafs
void leaf(Node* root){
if (root == NULL)
return;
stack<Node*> stc;
stc.push(root);
map<Node*, Node*> prnt;
prnt[root] = NULL;
while (!stc.empty()){
Node* curr = stc.top();
stc.pop();
if (!(curr->left) && !(curr->right))
calculatePath(curr, prnt);
if (curr->right){
prnt[curr->right] = curr;
stc.push(curr->right);
}
if (curr->left){
prnt[curr->left] = curr;
stc.push(curr->left);
}
}
}
int main(){
Node* root = newNode(67); //it will insert the nodes to create a tree
root->left = newNode(34);
root->right = newNode(89);
root->left->left = newNode(23);
root->left->right = newNode(95);
root->right->left = newNode(12);
leaf(root); //call the function leaf
return 0;
}Output
if we run the above program then it will generate the following output
67 34 23 67 34 95 67 89 12
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