【leetcode】257. Binary Tree Paths

来源：互联网发布：中国人口密度数据编辑：程序博客网时间：2024/04/27 16:45

题目要求：

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"]

给一颗二叉树，返回根节点到叶子结点的路径

思路：

用一个map储存每个结点的路径

/** * 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 LinkedList<String>();        if(root==null)        {            return result;        }        //定义一个stack用来遍历结点        Stack<TreeNode> stack = new Stack<TreeNode>();        stack.push(root);        //map 的key是当前结点，val是路径        Map<TreeNode,String> path = new HashMap<TreeNode,String>();        path.put(root,root.val+"");        while(!stack.isEmpty())        {            TreeNode temp = stack.pop();            if(temp.left==null&&temp.right==null)            {                result.add(path.get(temp));            }            if(temp.left!=null)            {                stack.push(temp.left);                path.put(temp.left,path.get(temp)+"->"+temp.left.val+"");            }            if(temp.right!=null)            {                stack.push(temp.right);                path.put(temp.right,path.get(temp)+"->"+temp.right.val+"");            }                  }        return result;    }}

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