草稿图网站
java的Deque

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

/*** 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;elsereturn 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;elsebreak;}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

/*** 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);elsepre.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

/*** 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