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Commitbed3394

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Merge pull requestyoungyangyang04#449 from KailokFung/master
feat(二叉树理论基础.md): 新增java版本
2 parentsc41cb46 +59403e0 commitbed3394

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3 files changed

+89
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lines changed

3 files changed

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‎problems/0226.翻转二叉树.md

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@@ -205,6 +205,7 @@ public:
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Java：
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```Java
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//DFS递归
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classSolution {
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/**
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* 前后序遍历都可以
@@ -226,6 +227,31 @@ class Solution {
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root.right= tmp;
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}
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}
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//BFS
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classSolution {
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publicTreeNodeinvertTree(TreeNoderoot) {
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if (root==null) {returnnull;}
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ArrayDeque<TreeNode> deque=newArrayDeque<>();
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deque.offer(root);
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while (!deque.isEmpty()) {
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int size= deque.size();
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while (size-->0) {
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TreeNode node= deque.poll();
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swap(node);
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if (node.left!=null) {deque.offer(node.left);}
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if (node.right!=null) {deque.offer(node.right);}
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}
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}
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return root;
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}
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publicvoidswap(TreeNoderoot) {
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TreeNode temp= root.left;
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root.left= root.right;
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root.right= temp;
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}
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}
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```
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Python：

‎problems/0257.二叉树的所有路径.md

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@@ -283,6 +283,7 @@ public:
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Java：
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```Java
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//解法一
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classSolution {
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/**
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* 递归法
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}
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}
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//解法二（常规前序遍历，不用回溯），更容易理解
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classSolution {
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publicList<String>binaryTreePaths(TreeNoderoot) {
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List<String> res=newArrayList<>();
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helper(root,newStringBuilder(), res);
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return res;
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}
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publicvoidhelper(TreeNoderoot,StringBuildersb,List<String>res) {
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if (root==null) {return;}
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// 遇到叶子结点就放入当前路径到res集合中
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if (root.left==null&& root.right==null) {
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sb.append(root.val);
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res.add(sb.toString());
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// 记得结束当前方法
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return;
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}
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helper(root.left,newStringBuilder(sb).append(root.val+"->"),res);
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helper(root.right,newStringBuilder(sb).append(root.val+"->"),res);
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}
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}
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//针对解法二优化，思路本质是一样的
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classSolution {
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publicList<String>binaryTreePaths(TreeNoderoot) {
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List<String> res=newArrayList<>();
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helper(root,"", res);
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return res;
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}
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publicvoidhelper(TreeNoderoot,Stringpath,List<String>res) {
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if (root==null) {return;}
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// 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
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StringBuilder sb=newStringBuilder(path);
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sb.append(root.val);
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if (root.left==null&& root.right==null) {
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res.add(sb.toString());
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}else{
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// 如果是非叶子结点则还需要跟上一个 “->”
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sb.append("->");
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helper(root.left,sb.toString(),res);
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helper(root.right,sb.toString(),res);
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}
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}
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}
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```
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Python：
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```
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Go：
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```go
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funcbinaryTreePaths(root *TreeNode) []string {
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res:=make([]string,0)

‎problems/二叉树理论基础.md

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@@ -188,6 +188,21 @@ struct TreeNode {
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Java：
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```java
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publicclassTreeNode {
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int val;
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TreeNode left;
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TreeNode right;
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TreeNode() {}
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TreeNode(intval) {this.val= val; }
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TreeNode(intval,TreeNodeleft,TreeNoderight) {
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this.val= val;
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this.left= left;
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this.right= right;
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}
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}
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```
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Python：
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