105 lines
2.1 KiB
Go
105 lines
2.1 KiB
Go
package top100liked
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// https://leetcode.cn/problems/lowest-common-ancestor-of-a-binary-tree/?envType=study-plan-v2&envId=top-100-liked
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type TreeNode struct {
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Val int
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Left *TreeNode
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Right *TreeNode
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}
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func buildTree(arr []*int) *TreeNode {
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if len(arr) == 0 || arr[0] == nil {
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return nil
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}
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root := &TreeNode{Val: *arr[0]}
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queue := []*TreeNode{root}
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i := 1
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for len(queue) > 0 && i < len(arr) {
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node := queue[0]
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queue = queue[1:]
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// 处理左孩子
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if i < len(arr) {
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if arr[i] != nil {
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node.Left = &TreeNode{Val: *arr[i]}
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queue = append(queue, node.Left)
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}
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i++
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}
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// 处理右孩子
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if i < len(arr) {
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if arr[i] != nil {
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node.Right = &TreeNode{Val: *arr[i]}
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queue = append(queue, node.Right)
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}
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i++
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}
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}
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return root
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}
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// // getParents 包括自身
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// func getParents(root *TreeNode, target int) []*TreeNode {
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// parents := []*TreeNode{}
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// var res []*TreeNode
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// var helper func(root *TreeNode) bool
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// helper = func(root *TreeNode) bool {
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// if root == nil {
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// return false
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// }
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// if root.Val == target {
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// res = append([]*TreeNode{}, parents...)
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// res = append(res, root)
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// return true
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// }
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// parents = append(parents, root)
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// if helper(root.Left) {
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// return true
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// }
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// if helper(root.Right) {
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// return true
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// }
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// parents = parents[:len(parents)-1]
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// return false
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// }
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// helper(root)
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// return res
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// }
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// // 朴素解法，AC，但效率很低
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// func lowestCommonAncestor(root, p, q *TreeNode) *TreeNode {
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// p1 := getParents(root, p.Val)
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// p2 := getParents(root, q.Val)
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// for i := len(p1) - 1; i >= 0; i-- {
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// for j := len(p2) - 1; j >= 0; j-- {
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// if p1[i].Val == p2[j].Val {
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// return p1[i]
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// }
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// }
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// }
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// return nil
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// }
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func lowestCommonAncestor(root, p, q *TreeNode) *TreeNode {
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var dfs func(*TreeNode) *TreeNode
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dfs = func(node *TreeNode) *TreeNode {
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if node == nil || node == p || node == q {
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return node
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}
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left := dfs(node.Left)
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right := dfs(node.Right)
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if left != nil && right != nil {
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return node
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}
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if left != nil {
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return left
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}
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return right
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}
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return dfs(root)
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}
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