JavaArithmetic/src/LeetCode/LeetCode257.java at master · git-jhy/JavaArithmetic · GitHub

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package LeetCode;

import java.util.ArrayList;

import java.util.List;

public class LeetCode257 {

/// 257. Binary Tree Paths

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

/// 时间复杂度: O(n), n为树中的节点个数

/// 空间复杂度: O(h), h为树的高度

// Definition for a binary tree node.

public class TreeNode {

int val;

TreeNode left;

TreeNode right;

TreeNode(int x) {

val = x;

}

/**

* 从底一直往上加

* @param root

* @return

public List<String> binaryTreePaths(TreeNode root) {

ArrayList<String> res = new ArrayList<>();

if (root == null)

return res;

// 比如 1

// /

// 2

if (root.left == null && root.right == null) {

res.add(Integer.toString(root.val));

return res;

}

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

for (String s : leftPaths) {

StringBuilder sb = new StringBuilder(Integer.toString(root.val));

sb.append("->");

sb.append(s);

res.add(sb.toString());

}

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

for (String s : rightPaths) {

StringBuilder sb = new StringBuilder(Integer.toString(root.val));

sb.append("->");

sb.append(s);

res.add(sb.toString());

}

return res;

}

JavaArithmetic/src/LeetCode/LeetCode257.java at master · git-jhy/JavaArithmetic · GitHub

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