Add solution 701

website/content/ChapterFour/0700~0799/0701.Insert-into-a-Binary-Search-Tree.md

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+# [701. Insert into a Binary Search Tree](https://leetcode.com/problems/insert-into-a-binary-search-tree/)
+
+
+## 题目
+
+You are given the `root` node of a binary search tree (BST) and a `value` to insert into the tree. Return *the root node of the BST after the insertion*. It is **guaranteed** that the new value does not exist in the original BST.
+
+**Notice** that there may exist multiple valid ways for the insertion, as long as the tree remains a BST after insertion. You can return **any of them**.
+
+**Example 1:**
+
+![https://assets.leetcode.com/uploads/2020/10/05/insertbst.jpg](https://assets.leetcode.com/uploads/2020/10/05/insertbst.jpg)
+
+```
+Input: root = [4,2,7,1,3], val = 5
+Output: [4,2,7,1,3,5]
+Explanation: Another accepted tree is:
+
+```
+
+![https://assets.leetcode.com/uploads/2020/10/05/bst.jpg](https://assets.leetcode.com/uploads/2020/10/05/bst.jpg)
+
+**Example 2:**
+
+```
+Input: root = [40,20,60,10,30,50,70], val = 25
+Output: [40,20,60,10,30,50,70,null,null,25]
+
+```
+
+**Example 3:**
+
+```
+Input: root = [4,2,7,1,3,null,null,null,null,null,null], val = 5
+Output: [4,2,7,1,3,5]
+
+```
+
+**Constraints:**
+
+- The number of nodes in the tree will be in the range `[0, 104]`.
+- `108 <= Node.val <= 108`
+- All the values `Node.val` are **unique**.
+- `108 <= val <= 108`
+- It's **guaranteed** that `val` does not exist in the original BST.
+
+## 题目大意
+
+给定二叉搜索树（BST）的根节点和要插入树中的值，将值插入二叉搜索树。 返回插入后二叉搜索树的根节点。 输入数据 保证 ，新值和原始二叉搜索树中的任意节点值都不同。注意，可能存在多种有效的插入方式，只要树在插入后仍保持为二叉搜索树即可。 你可以返回 任意有效的结果 。
+
+## 解题思路
+
+- 简单题。插入节点的方法有多种，笔者这里选择一种简单的方法。从根开始遍历这个二叉树，当前节点的值比待插入节点的值小，则往右遍历；当前节点的值比待插入节点的值大，则往左遍历。最后遍历到空节点便是要插入的地方。
+
+## 代码
+
+```go
+package leetcode
+
+import "github.com/halfrost/LeetCode-Go/structures"
+
+// TreeNode define
+type TreeNode = structures.TreeNode
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func insert(n *TreeNode, val int) *TreeNode {
+	if n == nil {
+		return &TreeNode{Val: val}
+	}
+	if n.Val < val {
+		n.Right = insert(n.Right, val)
+	} else {
+		n.Left = insert(n.Left, val)
+	}
+	return n
+}
+
+func insertIntoBST(root *TreeNode, val int) *TreeNode {
+	return insert(root, val)
+}
+```
+
+
+----------------------------------------------
+<div style="display: flex;justify-content: space-between;align-items: center;">
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