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@@ -0,0 +1,83 @@
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+package main
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+
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+// Invariant: both children are bigger
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+
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+type prioq struct {
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+ bintree []Car
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+}
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+
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+func (pq *prioq) Add(car Car) {
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+ pq.bintree = append(pq.bintree, car)
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+
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+ // Rebalance tree to respect invariant
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+ var i = len(pq.bintree) - 1
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+ var p = (i - 1) / 2
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+ for p >= 0 && pq.bintree[p].Arrival > pq.bintree[i].Arrival {
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+ pq.bintree[p], pq.bintree[i] = pq.bintree[i], pq.bintree[p]
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+ i = p
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+ p = (i - 1) / 2
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+ }
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+}
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+
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+func (pq *prioq) pop() Car {
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+ if len(pq.bintree) == 0 {
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+ panic("Trying to remove from empty queue")
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+ }
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+
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+ if len(pq.bintree) == 1 {
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+ elem := pq.bintree[0]
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+ pq.bintree = pq.bintree[:0]
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+ return elem
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+ }
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+
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+ elem := pq.bintree[0]
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+ // Put last element at root
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+ pq.bintree[0] = pq.bintree[len(pq.bintree)-1]
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+ // Remove last element
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+ pq.bintree = pq.bintree[:len(pq.bintree)-1]
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+
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+ // 1 9
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+ // 10 9 10 12
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+ // 11 12 13 14 -> 11 12 13 14
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+ // 12
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+
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+ // Rebalance tree to respect invariant
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+ len := len(pq.bintree)
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+ i, left, right := 0, 0, 0
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+ for {
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+ left = 2*i + 1
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+ right = 2*i + 2
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+ if left < len && right < len { // Two children
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+ if pq.bintree[left].Arrival <= pq.bintree[right].Arrival {
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+ if pq.bintree[i].Arrival <= pq.bintree[left].Arrival {
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+ break // Inferior to both children
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+ } else {
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+ pq.bintree[i], pq.bintree[left] = pq.bintree[left], pq.bintree[i]
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+ i = left
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+ }
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+ } else {
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+ if pq.bintree[i].Arrival <= pq.bintree[right].Arrival {
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+ break // Inferior to both children
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+ } else {
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+ pq.bintree[i], pq.bintree[right] = pq.bintree[right], pq.bintree[i]
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+ i = right
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+ }
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+ }
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+ } else if left < len { // One child (left)
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+ if pq.bintree[i].Arrival <= pq.bintree[left].Arrival {
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+ break // Inferior to only child
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+ }
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+ pq.bintree[i], pq.bintree[left] = pq.bintree[left], pq.bintree[i]
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+ i = left
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+ } else { // No child
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+ break
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+ }
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+
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+ }
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+
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+ return elem
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+}
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+
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+func (pq *prioq) empty() bool {
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+ return len(pq.bintree) == 0
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+}
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