Binary Tree Paths(lintcode 480)

Description

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

Example

Given the following binary tree:

    1
   / \
  2   3
   \
    5

All root-to-leaf paths are:

[
  "1->2->5",
  "1->3"
]

Interface

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root the root of the binary tree
     * @return all root-to-leaf paths
     */
    public List<String> binaryTreePaths(TreeNode root) {
        // Write your code here
    }
}

Solution

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root the root of the binary tree
     * @return all root-to-leaf paths
     */
    private List<String> result = new ArrayList<String>();

    public List<String> binaryTreePaths(TreeNode root) {
        // Write your code here
        traverse(root, "");
        return result;
    }

    private void traverse(TreeNode root, String path) {
        if (root == null) {
            return;
        }

        if (root.left == null && root.right == null) {
            path += root.val;
            result.add(path);
            return;
        }

        path += root.val;
        traverse(root.left, path + "->");
        traverse(root.right, path + "->");
    }
}