二叉树的所有路径

   1
 /   \
2     3
 \
  5

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

/**
 * 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) {
        List<String> paths = new ArrayList<String>();
        if (root == null) {
            return paths;
        }
        
        List<String> leftPaths = binaryTreePaths(root.left);
        List<String> rightPaths = binaryTreePaths(root.right);
        
        for (String path : leftPaths) {
            paths.add(root.val + "->" + path);
        }
        
        for (String path : rightPaths) {
            paths.add(root.val + "->" + path);
        }
        
        if (paths.size() == 0) {
            paths.add(String.valueOf(root.val));
        }
        
        return paths;
        
    }
}