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queue.go
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queue.go
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package main
import (
"container/heap"
)
// Node holds a stringified Board state and it's corresponding priority
type Node struct {
value string // The value of the node; arbitrary.
priority int // The priority of the node in the queue.
// The index is needed by update and is maintained by the heap.Interface methods.
index int // The index of the node in the heap.
}
// PriorityQueue implements heap.Interface and holds Nodes.
type PriorityQueue []*Node
func (pq PriorityQueue) Len() int { return len(pq) }
func (pq PriorityQueue) Less(i, j int) bool {
// We want Pop to give us the lowest, not highest,
// cost priority so we use less than here.
return pq[i].priority < pq[j].priority
}
// Swap ...
func (pq PriorityQueue) Swap(i, j int) {
pq[i], pq[j] = pq[j], pq[i]
pq[i].index = i
pq[j].index = j
}
// Push ...
func (pq *PriorityQueue) Push(x interface{}) {
n := len(*pq)
node := x.(*Node)
node.index = n
*pq = append(*pq, node)
}
// Pop ...
func (pq *PriorityQueue) Pop() interface{} {
old := *pq
n := len(old)
node := old[n-1]
node.index = -1 // for safety
*pq = old[0 : n-1]
return node
}
// Update modifies the priority and value of an Node in the queue.
func (pq *PriorityQueue) Update(node *Node, value string, priority int) {
node.value = value
node.priority = priority
heap.Fix(pq, node.index)
}