From 1a16c119a39f1929af9294b653385defa7c904f3 Mon Sep 17 00:00:00 2001 From: KailokFung Date: Sun, 27 Jun 2021 15:44:40 +0800 Subject: [PATCH 1/3] =?UTF-8?q?feat(=E4=BA=8C=E5=8F=89=E6=A0=91=E7=90=86?= =?UTF-8?q?=E8=AE=BA=E5=9F=BA=E7=A1=80.md):=20=E6=96=B0=E5=A2=9Ejava?= =?UTF-8?q?=E7=89=88=E6=9C=AC?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/二叉树理论基础.md | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/problems/二叉树理论基础.md b/problems/二叉树理论基础.md index 55383e91..d4dfe0c6 100644 --- a/problems/二叉树理论基础.md +++ b/problems/二叉树理论基础.md @@ -188,6 +188,21 @@ struct TreeNode { Java： +```java +public class TreeNode { + int val; + TreeNode left; + TreeNode right; + TreeNode() {} + TreeNode(int val) { this.val = val; } + TreeNode(int val, TreeNode left, TreeNode right) { + this.val = val; + this.left = left; + this.right = right; + } +} +``` + Python： From abc55ed100b031a00383038a3b7e2ee91c667b7a Mon Sep 17 00:00:00 2001 From: KailokFung Date: Tue, 29 Jun 2021 16:50:34 +0800 Subject: [PATCH 2/3] =?UTF-8?q?feat(0226):=20=E6=96=B0=E5=A2=9Ejava=20bfs?= =?UTF-8?q?=E5=86=99=E6=B3=95?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0226.翻转二叉树.md | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/problems/0226.翻转二叉树.md b/problems/0226.翻转二叉树.md index 2b628ec4..bb0d6d34 100644 --- a/problems/0226.翻转二叉树.md +++ b/problems/0226.翻转二叉树.md @@ -205,6 +205,7 @@ public: Java： ```Java +//DFS递归 class Solution { /** * 前后序遍历都可以 @@ -226,6 +227,31 @@ class Solution { root.right = tmp; } } + +//BFS +class Solution { + public TreeNode invertTree(TreeNode root) { + if (root == null) {return null;} + ArrayDeque deque = new ArrayDeque<>(); + deque.offer(root); + while (!deque.isEmpty()) { + int size = deque.size(); + while (size-- > 0) { + TreeNode node = deque.poll(); + swap(node); + if (node.left != null) {deque.offer(node.left);} + if (node.right != null) {deque.offer(node.right);} + } + } + return root; + } + + public void swap(TreeNode root) { + TreeNode temp = root.left; + root.left = root.right; + root.right = temp; + } +} ``` Python： From 59403e05819e659dd3a0566656774bc6dd48846e Mon Sep 17 00:00:00 2001 From: KailokFung Date: Sat, 3 Jul 2021 16:14:10 +0800 Subject: [PATCH 3/3] =?UTF-8?q?feat(0257):=20=E6=96=B0=E5=A2=9E=E4=B8=A4?= =?UTF-8?q?=E7=A7=8Djava=E8=A7=A3=E6=B3=95?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0257.二叉树的所有路径.md | 49 ++++++++++++++++++++++- 1 file changed, 48 insertions(+), 1 deletion(-) diff --git a/problems/0257.二叉树的所有路径.md b/problems/0257.二叉树的所有路径.md index d5a0478e..ce596396 100644 --- a/problems/0257.二叉树的所有路径.md +++ b/problems/0257.二叉树的所有路径.md @@ -283,6 +283,7 @@ public: Java： ```Java +//解法一 class Solution { /** * 递归法 @@ -321,6 +322,52 @@ class Solution { } } +//解法二（常规前序遍历，不用回溯），更容易理解 +class Solution { + public List binaryTreePaths(TreeNode root) { + List res = new ArrayList<>(); + helper(root, new StringBuilder(), res); + return res; + } + + public void helper(TreeNode root, StringBuilder sb, List res) { + if (root == null) {return;} + // 遇到叶子结点就放入当前路径到res集合中 + if (root.left == null && root.right ==null) { + sb.append(root.val); + res.add(sb.toString()); + // 记得结束当前方法 + return; + } + helper(root.left,new StringBuilder(sb).append(root.val + "->"),res); + helper(root.right,new StringBuilder(sb).append(root.val + "->"),res); + } +} + +//针对解法二优化，思路本质是一样的 +class Solution { + public List binaryTreePaths(TreeNode root) { + List res = new ArrayList<>(); + helper(root, "", res); + return res; + } + + public void helper(TreeNode root, String path, List res) { + if (root == null) {return;} + // 由原始解法二可以知道，root的值肯定会下面某一个条件加入到path中，那么干脆直接在这一步加入即可 + StringBuilder sb = new StringBuilder(path); + sb.append(root.val); + if (root.left == null && root.right ==null) { + res.add(sb.toString()); + }else{ + // 如果是非叶子结点则还需要跟上一个 “->” + sb.append("->"); + helper(root.left,sb.toString(),res); + helper(root.right,sb.toString(),res); + } + } +} + ``` Python： @@ -350,7 +397,7 @@ class Solution: ``` Go： - + ```go func binaryTreePaths(root *TreeNode) []string { res := make([]string, 0)