Merge pull request #236 from hk27xing/hk27xing-add

添加105和113题的Java代码
This commit is contained in:
Carl Sun
2021-05-24 18:02:17 +08:00
committed by GitHub
2 changed files with 75 additions and 1 deletions

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@ -580,8 +580,10 @@ tree2 的前序遍历是[1 2 3] 后序遍历是[3 2 1]。
## 其他语言版本
Java
106.从中序与后序遍历序列构造二叉树
```java
class Solution {
public TreeNode buildTree(int[] inorder, int[] postorder) {
@ -617,8 +619,43 @@ class Solution {
}
```
105.从前序与中序遍历序列构造二叉树
```java
class Solution {
public TreeNode buildTree(int[] preorder, int[] inorder) {
return helper(preorder, 0, preorder.length - 1, inorder, 0, inorder.length - 1);
}
public TreeNode helper(int[] preorder, int preLeft, int preRight,
int[] inorder, int inLeft, int inRight) {
// 递归终止条件
if (inLeft > inRight || preLeft > preRight) return null;
// val 为前序遍历第一个的值,也即是根节点的值
// idx 为根据根节点的值来找中序遍历的下标
int idx = inLeft, val = preorder[preLeft];
TreeNode root = new TreeNode(val);
for (int i = inLeft; i <= inRight; i++) {
if (inorder[i] == val) {
idx = i;
break;
}
}
// 根据 idx 来递归找左右子树
root.left = helper(preorder, preLeft + 1, preLeft + (idx - inLeft),
inorder, inLeft, idx - 1);
root.right = helper(preorder, preLeft + (idx - inLeft) + 1, preRight,
inorder, idx + 1, inRight);
return root;
}
}
```
Python
105.从前序与中序遍历序列构造二叉树
```python
# Definition for a binary tree node.
# class TreeNode:
@ -637,6 +674,7 @@ class Solution:
return root
```
106.从中序与后序遍历序列构造二叉树
```python
# Definition for a binary tree node.
# class TreeNode:

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@ -347,6 +347,42 @@ class Solution {
}
```
0113.路径总和-ii
```java
class Solution {
public List<List<Integer>> pathSum(TreeNode root, int targetSum) {
List<List<Integer>> res = new ArrayList<>();
if (root == null) return res; // 非空判断
List<Integer> path = new LinkedList<>();
preorderDFS(root, targetSum, res, path);
return res;
}
public void preorderDFS(TreeNode root, int targetSum, List<List<Integer>> res, List<Integer> path) {
path.add(root.val);
// 遇到了叶子节点
if (root.left == null && root.right == null) {
// 找到了和为 targetSum 的路径
if (targetSum - root.val == 0) {
res.add(new ArrayList<>(path));
}
return; // 如果和不为 targetSum返回
}
if (root.left != null) {
preorderDFS(root.left, targetSum - root.val, res, path);
path.remove(path.size() - 1); // 回溯
}
if (root.right != null) {
preorderDFS(root.right, targetSum - root.val, res, path);
path.remove(path.size() - 1); // 回溯
}
}
}
```
Python
0112.路径总和