Binary Tree Paths

Problem Description

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

For example, given the following binary tree:

   1
 /   \
2     3
 \
  5

All root-to-leaf paths are:

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

Solution
I. Java Solution

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<String> binaryTreePaths(TreeNode root) {
        List<String> result = new ArrayList<String>();
        
        if(root == null) return result;
        LinkedList<TreeNode> path = new LinkedList<TreeNode>();
        
        path.push(root);
        
        TreeNode temp;
        while(!path.isEmpty()){
            temp = path.peek();
            if(temp.left != null){
                path.push(temp.left);
            }else if(temp.right != null){
                path.push(temp.right);
            }else{
                result.add(listToString(path));
                temp = path.pop();
                while(!path.isEmpty()){
                    if(path.peek().left == temp
                        && path.peek().right!=null){
                        path.push(path.peek().right);
                        break;
                    }
                    temp = path.pop();
                }
            }
            
        }
    
        return result;
    }
    
    public String listToString(LinkedList<TreeNode> path){
        ListIterator<TreeNode> iterator = path.listIterator(path.size());
        StringBuilder builder = new StringBuilder();
        builder.append(iterator.previous().val);
        while(iterator.hasPrevious()){
            builder.append("->" + iterator.previous().val);
        }
        return builder.toString();
    }
}