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算法的重要性，我就不多說了吧，想去大廠，就必須要經(jīng)過基礎知識和業(yè)務邏輯面試+算法面試。所以，為了提高大家的算法能力，這個公眾號后續(xù)每天帶大家做一道算法題，題目就從LeetCode上面選！

今天和大家聊的問題叫做 二叉樹的所有路徑，我們先來看題面：

https://leetcode-cn.com/problems/binary-tree-paths/

Given the root of a binary tree, return all root-to-leaf paths in any order.
A leaf is a node with no children.

給定一個二叉樹，返回所有從根節(jié)點到葉子節(jié)點的路徑。說明: 葉子節(jié)點是指沒有子節(jié)點的節(jié)點。

解題

/**
 * 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> list = new LinkedList<>();
        helper(root, "", list);
        return list;
    }
    
    private void helper(TreeNode root, String s, List<String>list){
        if (root == null){
            return;
        }
        
        s = s + root.val;
        
        if (root.left == null && root.right == null){
            list.add(s);
            return;
        }
        
        if (root.left != null){
            helper(root.left, s + "->", list);
        }

        if (root.right != null){
            helper(root.right, s + "->", list);
        }
    }
 
    
 
}