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lowest-common-ancestor-of-a-binary-tree.go
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lowest-common-ancestor-of-a-binary-tree.go
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// https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree
package leetcode
// Definition for a binary tree node.
type TreeNode struct {
Val int
Left *TreeNode
Right *TreeNode
}
// 效率低
func lowestCommonAncestorBT(root, p, q *TreeNode) *TreeNode {
l := hasNode(root.Left, p, q)
r := hasNode(root.Right, p, q)
if l == 1 && r == 1 {
return root
}
if l == 2 {
return lowestCommonAncestorBT(root.Left, p, q)
}
if r == 2 {
return lowestCommonAncestorBT(root.Right, p, q)
}
if root.Val == p.Val || root.Val == q.Val {
return root
}
return nil
}
func hasNode(root, p, q *TreeNode) int {
if root == nil {
return 0
}
var i int
if root.Val == p.Val {
i++
}
if root.Val == q.Val {
i++
}
i += hasNode(root.Left, p, q)
i += hasNode(root.Right, p, q)
return i
}
// 效率高
func lowestCommonAncestorBT2(root, p, q *TreeNode) *TreeNode {
if root == nil {
return nil
}
if root.Val == q.Val || root.Val == p.Val {
return root
}
l := lowestCommonAncestor(root.Left, p, q)
r := lowestCommonAncestor(root.Right, p, q)
if l == nil {
return r
} else {
if r == nil {
return l
} else {
return root
}
}
}
func lowestCommonAncestor(root, p, q *TreeNode) *TreeNode {
if root == nil {
return nil
}
if (p.Val <= root.Val && root.Val <= q.Val) || (p.Val >= root.Val && root.Val >= q.Val) {
return root
}
if root.Left != nil {
l := lowestCommonAncestor(root.Left, p, q)
if l != nil {
return l
}
}
if root.Right != nil {
r := lowestCommonAncestor(root.Right, p, q)
if r != nil {
return r
}
}
return nil
}