Recursive-Inorder_Preorder_PostOrder_Traversal

package com.tree.traversal;

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

public class PreorderTraversal {

	static List<Integer> result;

	public static void main(String[] args) {
		TreeNode left = new TreeNode(2);
		TreeNode right = new TreeNode(3);
		TreeNode root = new TreeNode(1, left, right);
		left.left = new TreeNode(4);
		left.right = new TreeNode(5);
		right.left = new TreeNode(6);
		right.right = new TreeNode(7);

		result = new ArrayList<Integer>();
		System.out.println("Preorder Traversal : " + preorderTraversal(root));
		result = new ArrayList<Integer>();
		System.out.println("Inorder Traversal : " + inorderTraversal(root));
		result = new ArrayList<Integer>();
		System.out.println("Postorder Traversal : " + postorderTraversal(root));
	}

	public static List<Integer> preorderTraversal(TreeNode root) {
		if (root != null) {
			result.add(root.val);
			preorderTraversal(root.left);
			preorderTraversal(root.right);
		}
		return result;
	}
	
	public static List<Integer> inorderTraversal(TreeNode root) {
		if (root != null) {
			inorderTraversal(root.left);
			result.add(root.val);
			inorderTraversal(root.right);
		}
		return result;
	}
	
	public static List<Integer> postorderTraversal(TreeNode root) {
		if (root != null) {
			postorderTraversal(root.left);
			postorderTraversal(root.right);
			result.add(root.val);
		}
		return result;
	}
}

class TreeNode {
	int val;
	TreeNode left;
	TreeNode right;

	TreeNode() {
	}

	TreeNode(int val) {
		this.val = val;
	}

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