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77 lines
1.4 KiB
Go
77 lines
1.4 KiB
Go
package regex
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import "container/heap"
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// Implement a priority queue using container/heap
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const (
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min_priority int = iota
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zerostate_priority
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alternation_priority
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kleene_priority
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char_priority
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max_priority
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)
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func getPriority(state *nfaState) int {
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if state.isKleene {
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return kleene_priority
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} else if state.isQuestion || state.isAlternation {
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return alternation_priority
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} else {
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if state.isEmpty {
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return zerostate_priority
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} else {
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return char_priority
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}
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}
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}
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type priorQueueItem struct {
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state *nfaState
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priority int
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index int
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}
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type priorityQueue []*priorQueueItem
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func (pq priorityQueue) Len() int {
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return len(pq)
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}
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func (pq priorityQueue) Less(i, j int) bool {
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if pq[i].priority == pq[j].priority {
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return pq[i].index > pq[j].index
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}
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return pq[i].priority > pq[j].priority // We want max-heap, so we use greater-than
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}
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func (pq priorityQueue) Swap(i, j int) {
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pq[i], pq[j] = pq[j], pq[i]
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pq[i].index = i
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pq[j].index = j
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}
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func (pq *priorityQueue) Push(x any) {
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length := len(*pq)
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item := x.(*priorQueueItem)
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item.index = length
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*pq = append(*pq, item)
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}
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func (pq *priorityQueue) Pop() any {
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old := *pq
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n := len(old)
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item := old[n-1]
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old[n-1] = nil
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item.index = -1
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*pq = old[0 : n-1]
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return item
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}
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func (pq *priorityQueue) update(item *priorQueueItem, value *nfaState, priority int) {
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item.state = value
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item.priority = priority
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heap.Fix(pq, item.index)
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}
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