257. Binary Tree Paths

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”]

>

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<String> binaryTreePaths(TreeNode root) {
        List<String> allPaths=new ArrayList<String>();
        if(root==null) return allPaths;
        if(root.left==null&&root.right==null){//容易忽略
            allPaths.add(root.val+"");//将int转为string
            return allPaths;
        }

        List<String> left=binaryTreePaths(root.left);
        List<String> right=binaryTreePaths(root.right);

        for(String item1:left){
            item1=root.val+"->"+item1;
            allPaths.add(item1);//不能再外面加
        }
        for(String item2:right){
             item2=root.val+"->"+item2;
             allPaths.add(item2);//不能再外面加
        }
        return allPaths;
    }
}