http://www.lintcode.com/en/problem/binary-tree-paths/

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"
]

解题：要求所有从root到leaf的路径，一般的遍历都可以，注意处理一下结果需要的字符串就好了。

public class Solution {
    public List<String> binaryTreePaths(TreeNode root) {
        List<String> result = new ArrayList<String>();
        if (root != null) {
            findPath(result, root, String.valueOf(root.val));
        }
        return result;
    }

    public void findPath(List<String> result, TreeNode p, String path) {
        if(p == null) {
            return ;
        }
        //到leaf，左右都为空的时候
        if (p.left == null && p.right == null) {
            result.add(path);  
            return ;
        }
        //左子树不为空的时候
        if(p.left != null) {
            findPath(result, p.left, path + "->" + String.valueOf(p.left.val));
        }
        //右子树不为空的时候
        if(p.right != null) {
            findPath(result, p.right, path + "->" + String.valueOf(p.right.val));
        }
    }
}