CodePost-OrderTraversal.java

// Code : Post-order Traversal
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// Given a generic tree, print the post-order traversal of given tree.
// The post-order traversal is: visit child nodes first and then root node.

// For the given tree, the post order traversal will be 40 50 20 30 40 10
// Input format:
// The first line of input contains data of the nodes of the tree in level order
// form. The order is: data for root node, number of children to root node, data
// of each of child nodes and so on and so forth for each node. The data of the
// nodes of the tree is separated by space.
// Output Format :
// The first and only line of output contains the elements printed in post-order
// traversal. The elements in the output must be separated by a single space.
// Constraints:
// Time Limit: 1 sec
// Sample Input 1:
// 10 3 20 30 40 2 400 50 0 0 0 0
// Sample Output 1:
// 400 50 20 30 40 10
// Explanation
// For 10 , total 3 children are there : 20 30 40
// For 20, total 2 children are there : 400 50
// So, the output will be 400 50 20 30 40 10

public class Solution {

    /*
     * TreeNode structure
     * 
     * class TreeNode<T> {
     * T data;
     * ArrayList<TreeNode<T>> children;
     * 
     * TreeNode(T data){
     * this.data = data;
     * children = new ArrayList<TreeNode<T>>();
     * }
     * }
     */

    public static void printPostOrder(TreeNode<Integer> root) {
        /*
         * Your class should be named Solution.
         * Don't write main() function.
         * Don't read input, it is passed as function argument.
         * Print output as specified in the question
         */
        if (root == null) {
            return;
        }

        for (int i = 0; i < root.children.size(); i++) {
            printPostOrder(root.children.get(i));
        }
        System.out.print(root.data + " ");
    }

}