72 lines
2.1 KiB
Go
72 lines
2.1 KiB
Go
/*
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Copyright 2024.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package helper
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// DetectGraphCycle checks if there is a cycle involving a given node in directed graph
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//
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// Assumptions:
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// - all nodes have AT MOST one OUTGOING edge
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//
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// Parameters:
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// - startNode: the node to start the cycle detection from
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// - checkedNodes: a map of nodes which have already been checked for cycles (updated in-place if no cycle is detected)
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// - edgeMap: a map representing the edges in the graph
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//
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// Returns:
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// - returns nil, if no cycle is detected
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// - returns a slice of nodes representing the cycle, if a cycle is detected
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func DetectGraphCycle(startNode string, checkedNodes map[string]bool, edgeMap map[string]string) []string {
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currentPath := make([]string, 0)
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currentPathNodes := make(map[string]bool)
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var currentNode = startNode
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for {
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// if the current node has already been checked, no cycle is detected
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if checkedNodes[currentNode] {
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break
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}
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// if the current node is already in the current path, a cycle is detected
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if currentPathNodes[currentNode] {
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for i, node := range currentPath {
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// the cycle starts from the first occurrence of the current node
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if node == currentNode {
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return currentPath[i:]
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}
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}
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}
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// add the current node to the current path
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currentPath = append(currentPath, currentNode)
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currentPathNodes[currentNode] = true
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// get the next node
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nextNode, exists := edgeMap[currentNode]
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if !exists {
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// if there is no outgoing edge, no cycle is detected
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break
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}
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currentNode = nextNode
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}
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// mark all nodes in the current path as checked
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for node := range currentPathNodes {
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checkedNodes[node] = true
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}
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return nil
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}
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