LeetCode题目

235.二叉搜索树的最近公共祖先

题目链接：Lowest Common Ancestor of a Binary Search Tree - LeetCode

代码如下：

递归法

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val   int
 *     Left  *TreeNode
 *     Right *TreeNode
 * }
 */

func lowestCommonAncestor(root, p, q *TreeNode) *TreeNode {
	if root.Val > p.Val && root.Val > q.Val {
		return lowestCommonAncestor(root.Left, p, q)
	} else if root.Val < p.Val && root.Val < q.Val {
		return lowestCommonAncestor(root.Right, p, q)
	} else {
		return root
	}
}

迭代法

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val   int
 *     Left  *TreeNode
 *     Right *TreeNode
 * }
 */

func lowestCommonAncestor(root, p, q *TreeNode) *TreeNode {
	for root != nil {
		if root.Val > p.Val && root.Val > q.Val {
			root = root.Left
		} else if root.Val < p.Val && root.Val < q.Val {
			root = root.Right
		} else {
			return root
		}
	}
	return nil
}

701.二叉搜索树中的插入操作

题目链接：Insert into a Binary Search Tree - LeetCode

代码如下：

递归法

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func insertIntoBST(root *TreeNode, val int) *TreeNode {
	if root == nil {
		root = &TreeNode{Val: val}
		return root
	}
	if root.Val > val {
		root.Left = insertIntoBST(root.Left, val)
	} else {
		root.Right = insertIntoBST(root.Right, val)
	}
	return root
}

迭代法

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func insertIntoBST(root *TreeNode, val int) *TreeNode {
	cur := root
	node := &TreeNode{
		Val:   val,
		Left:  nil,
		Right: nil,
	}
	if cur == nil {
		root = node
		return root
	}
	var pre *TreeNode = nil
	for cur != nil {
		if cur.Val == val {
			return root
		}
		pre = cur
		if cur.Val < val {
			cur = cur.Right
		} else {
			cur = cur.Left
		}
	}
	if pre.Val < val {
		pre.Right = node
	} else {
		pre.Left = node
	}
	return root
}

450.删除二叉搜索树中的节点

题目链接：Delete Node in a BST - LeetCode

代码如下：

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func deleteNode(root *TreeNode, key int) *TreeNode {
	if root == nil {
		return root
	}
	if key < root.Val {
		root.Left = deleteNode(root.Left, key)
		return root
	}
	if key > root.Val {
		root.Right = deleteNode(root.Right, key)
		return root
	}
	if root.Left == nil {
		return root.Right
	}
	if root.Right == nil {
		return root.Left
	}
	cur := root.Right
	for cur.Left != nil {
		cur = cur.Left
	}
	cur.Left = root.Left
	root = root.Right
	return root
}