文章目录
Leetcode 235. 二叉搜索树的最近公共祖先
题目: 235. 二叉搜索树的最近公共祖先
解析: 代码随想录解析
解题思路
法1:和人二叉树的最近公共祖先一样的遍历搜索方法。
代码
java
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
if (root == null || root == p || root == q)
return root;
TreeNode left = lowestCommonAncestor(root.left, p, q);
TreeNode right = lowestCommonAncestor(root.right, p, q);
if (left == null &&right == null)
return null;
else if (left != null && right == null)
return left;
else if (left == null && right != null)
return right;
else
return root;
}
}
//递归
class Solution {
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
if (p.val < root.val && q.val < root.val) return lowestCommonAncestor(root.left, p, q);
if (p.val > root.val && q.val > root.val) return lowestCommonAncestor(root.right, p, q);
return root;
}
}
//迭代法
class Solution {
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
TreeNode cur = root;
while (true) {
if (p.val < cur.val && q.val < cur.val)
cur = cur.left;
else if (p.val > cur.val && q.val > cur.val)
cur = cur.right;
else
break;
}
return cur;
}
}
总结
利用好二叉搜索树的有序性
Leetcode 701. 二叉搜索树中的插入操作
题目: 701. 二叉搜索树中的插入操作
解析: 代码随想录解析
解题思路
迭代和递归
代码
java
/**
* Definition for a binary tree node.
* 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;
* }
* }
*/
class Solution {
public TreeNode insertIntoBST(TreeNode root, int val) {
if (root == null)
return new TreeNode(val);
TreeNode pre = null;
TreeNode cur = root;
while (cur != null) {
if (val < cur.val) {
pre = cur;
cur = cur.left;
} else if (val > cur.val) {
pre = cur;
cur = cur.right;
}
}
if (val < pre.val)
pre.left = new TreeNode(val);
else
pre.right = new TreeNode(val);
return root;
}
}
//递归
class Solution {
public TreeNode insertIntoBST(TreeNode root, int val) {
if (root == null)
return new TreeNode(val);
if (val < root.val)
root.left = insertIntoBST(root.left, val);
if (val > root.val)
root.right = insertIntoBST(root.right, val);
return root;
}
}
总结
根据二叉搜索树的性质
Leetcode 450. 删除二叉搜索树中的节点
题目: 450. 删除二叉搜索树中的节点
解析: 代码随想录解析
解题思路
应该为左为空,右为空,左右都不为空的情况
代码
java
/**
* Definition for a binary tree node.
* 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;
* }
* }
*/
class Solution {
public TreeNode deleteNode(TreeNode root, int key) {
if (root == null)
return root;
if (root.val == key) {
if (root.left == null)
return root.right;
else if (root.right == null)
return root.left;
else{
TreeNode cur = root.left;
while (cur.right != null)
cur = cur.right;
cur.right = root.right;
root = root.left;
return root;
}
}
if (key < root.val) root.left = deleteNode(root.left, key);
if (key > root.val) root.right = deleteNode(root.right, key);
return root;
}
}
总结
暂无