Binary Tree Paths – Given a binary tree, return all root-to-leaf paths.

Problem.

Given a binary tree, return all root-to-leaf paths.

Given Tree

 

Print all the root-to-leaf path

• 1->2->3
• 1->2->5
• 1->3

Solution

TreeNode Data Structure

package com.programtalk.learn.interview.questions;
class TreeNode {
	TreeNode left, right;
	int val;

	TreeNode(int val) {
		this.val = val;
		left = right = null;
	}
}

Binary Tree Solution

package com.programtalk.learn.interview.questions;

import java.util.ArrayList;
import java.util.List;

public class BinaryTreePath2Root {

	public List<List<Integer>> binaryTreePaths(TreeNode root) {
		List<List<Integer>> answer = new ArrayList<List<Integer>>();
		if (root != null){
			searchBT(root, new ArrayList<Integer>(), answer);
		}
		return answer;
	}

	private void searchBT(TreeNode root, List<Integer> currentPath, List<List<Integer>> allPaths) {
		currentPath.add(root.val);
		if (root.left == null && root.right == null){
			allPaths.add(currentPath);
			return;
		}
		
		if (root.left != null){
			searchBT(root.left,  new ArrayList<>(currentPath), allPaths);
		}
		
		if (root.right != null){
			searchBT(root.right,  new ArrayList<>(currentPath), allPaths);
		}
	}
	
	public static void main(String args[]) {
		BinaryTreePath2Root tree = new BinaryTreePath2Root();
		TreeNode  root = new TreeNode(1);
		root.left = new TreeNode(2);
		root.right = new TreeNode(3);
		root.left.left = new TreeNode(4);
		root.left.right = new TreeNode(5);

		System.out.println(tree.binaryTreePaths(root));
	}
}

OutPut

[[1, 2, 4], [1, 2, 5], [1, 3]]