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Zigzag tree traversal

Sourav das
I am a computer science student and a full stack coder
・2 min read

In this article I will show you how to traverse a tree in zigzag manner

// zigzag trav for tree

            --->
//           12
//         /    \
        <------------
//        9      15
//       / \
      ------------>
//      4   10

// output :- 12 15 9 4 10

#include<iostream>
#include<stack>
using namespace std;
class Node
{
public:
    int data;
    Node *right,*left;
    Node(int data)
    {
        this->data=data;
        right=left=NULL;
    }
};
void zigzagtrav(Node *root)
{
    stack<Node*> curr;
    stack<Node*> next;
    bool leftToright=true;
    curr.push(root);
    while(!curr.empty())
    {
        Node *tmp=curr.top();
        curr.pop();
        if(tmp)
        {
            cout<<tmp->data<<" ";
            if(leftToright)
            {
                next.push(tmp->left);
                next.push(tmp->right);
            }
            else
            {
                next.push(tmp->right);
                next.push(tmp->left);
            }
        }
        if(curr.empty())
        {
            leftToright=!leftToright;
            swap(curr,next);
        }
    }
}
int main()
{   
    #ifndef ONLINE_JUDGE
        freopen("../input.txt", "r", stdin);
        freopen("../output.txt", "w", stdout);
    #endif
    Node *root=new Node(12);
    root->right=new Node(15);
    root->left=new Node(9);
    root->left->left=new Node(4);
    root->left->right=new Node(10);
    zigzagtrav(root);
    return 0;
}
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here we are using two stacks

  1. curr which is to store our current node
  2. next which is to store the next node
  3. here the leftToright is to check that are we are printing the nodes left-to-right or right-to-left if the variable is true then we are printing the nodes left to right else print right-to-left.
  4. Here if leftToright is true we are pushing the current left and then right node to next stack else push current right and then left node to next stack.
  5. and checking if the curr node is empty swap the stack with next stack and toggle the leftToright variable.

Do it until both stack is empty.

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