40 lines
1.3 KiB
Java
40 lines
1.3 KiB
Java
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package tree;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* 题目： 257. 二叉树的所有路径 ( binaryTreePaths)
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* 描述：给你一个二叉树的根节点 root ，按 任意顺序 ，返回所有从根节点到叶子节点的路径。
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* 叶子节点 是指没有子节点的节点。
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*
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* 示例 1：
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输入：root = [1,2,3,null,5]
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输出：["1->2->5","1->3"]
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* 链接：https://leetcode.cn/problems/binary-tree-paths/
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*/
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public class BinaryTreePaths {
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public List<String> binaryTreePaths(TreeNode root) {
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List<String> res = new ArrayList<>();
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if (root == null) return res;
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StringBuilder sb = new StringBuilder();
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dfs(root, sb, res);
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return res;
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}
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private void dfs(TreeNode node, StringBuilder sb, List<String> res) {
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int len = sb.length(); // 记录进入当前节点前的长度
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sb.append(node.val);
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// 如果是叶子节点
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if (node.left == null && node.right == null) {
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res.add(sb.toString());
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} else {
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sb.append("->");
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if (node.left != null) dfs(node.left, sb, res);
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if (node.right != null) dfs(node.right, sb, res);
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}
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sb.setLength(len); // 回溯：恢复到进入本节点前的状态
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}
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}
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