/
lca.go
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/
lca.go
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// Copyright (c) 2019 Matúš Mrekaj.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License
package binarytrees
// exists returns true if <node> is a node
// in the tree that starts at <root>
// Take O(N) time with O(h) space complexity.
func exists(node *Node, root *Node) bool {
if root == nil {
return false
}
return root == node || exists(node, root.Left) || exists(node, root.Right)
}
func lcahelper(root, node0, node1 *Node) (*Node, int) {
if root == nil {
return nil, 0
}
lt, cl := lcahelper(root.Left, node0, node1)
if cl == 2 {
return lt, cl
}
rt, cr := lcahelper(root.Right, node0, node1)
if cr == 2 {
return rt, cr
}
count := cl + cr
if root == node0 {
count++
}
if root == node1 {
count++
}
if count == 2 {
return root, count
}
return nil, count
}
// LCA finds the least common ancestor of two nodes
// in a binary tree. Returns nil if no LCA is found.
// Take O(N) time with O(h) space complexity.
func LCA(root, node0, node1 *Node) *Node {
r, _ := lcahelper(root, node0, node1)
return r
}