Revert "Prioq can now remove any element if its position is known"

This reverts commit e25b00cee82e185d0fe1447c64d07285a5fe5079.

main.go

@@ -65,7 +65,6 @@ func (rs ByEndtime) Less(i, j int) bool {
 
 type Scheduler interface {
 	Add(*Car)
-	RemoveAtIndex(k int) *Car
 	Pop() *Car
 }
 
@@ -77,8 +76,7 @@ type Car struct {
 	X       int
 	Y       int
 
-	score   int
-	pqindex int // used for removal in prority queue
+	score int
 }
 
 func (c *Car) Update(r *Ride) {
@@ -297,35 +295,31 @@ type prioq struct {
 
 func (pq *prioq) Add(car *Car) {
 	pq.bintree = append(pq.bintree, car)
-	pq.bintree[len(pq.bintree)-1].pqindex = len(pq.bintree) - 1
 
 	// Rebalance tree to respect invariant
 	var i = len(pq.bintree) - 1
 	var p = (i - 1) / 2
 	for p >= 0 && pq.bintree[p].Arrival > pq.bintree[i].Arrival {
 		pq.bintree[p], pq.bintree[i] = pq.bintree[i], pq.bintree[p]
-		pq.bintree[p].pqindex = p
-		pq.bintree[i].pqindex = i
 		i = p
 		p = (i - 1) / 2
 	}
 }
 
-func (pq *prioq) RemoveAtIndex(k int) *Car {
+func (pq *prioq) Pop() *Car {
 	if len(pq.bintree) == 0 {
 		return nil
 	}
 
-	if k == len(pq.bintree)-1 {
-		elem := pq.bintree[k]
-		pq.bintree = pq.bintree[:k]
+	if len(pq.bintree) == 1 {
+		elem := pq.bintree[0]
+		pq.bintree = pq.bintree[:0]
 		return elem
 	}
 
-	elem := pq.bintree[k]
-	// Put last element at hole
-	pq.bintree[k] = pq.bintree[len(pq.bintree)-1]
-	pq.bintree[k].pqindex = k
+	elem := pq.bintree[0]
+	// Put last element at root
+	pq.bintree[0] = pq.bintree[len(pq.bintree)-1]
 	// Remove last element
 	pq.bintree = pq.bintree[:len(pq.bintree)-1]
 
@@ -336,8 +330,7 @@ func (pq *prioq) RemoveAtIndex(k int) *Car {
 
 	// Rebalance tree to respect invariant
 	len := len(pq.bintree)
-	i := k
-	left, right := 0, 0
+	i, left, right := 0, 0, 0
 	for {
 		left = 2*i + 1
 		right = 2*i + 2
@@ -347,8 +340,6 @@ func (pq *prioq) RemoveAtIndex(k int) *Car {
 					break // Inferior to both children
 				} else {
 					pq.bintree[i], pq.bintree[left] = pq.bintree[left], pq.bintree[i]
-					pq.bintree[i].pqindex = i
-					pq.bintree[left].pqindex = left
 					i = left
 				}
 			} else {
@@ -356,8 +347,6 @@ func (pq *prioq) RemoveAtIndex(k int) *Car {
 					break // Inferior to both children
 				} else {
 					pq.bintree[i], pq.bintree[right] = pq.bintree[right], pq.bintree[i]
-					pq.bintree[i].pqindex = i
-					pq.bintree[right].pqindex = right
 					i = right
 				}
 			}
@@ -366,8 +355,6 @@ func (pq *prioq) RemoveAtIndex(k int) *Car {
 				break // Inferior to only child
 			}
 			pq.bintree[i], pq.bintree[left] = pq.bintree[left], pq.bintree[i]
-			pq.bintree[i].pqindex = i
-			pq.bintree[left].pqindex = left
 			i = left
 		} else { // No child
 			break
@@ -378,10 +365,6 @@ func (pq *prioq) RemoveAtIndex(k int) *Car {
 	return elem
 }
 
-func (pq *prioq) Pop() *Car {
-	return pq.RemoveAtIndex(0)
-}
-
 func (pq *prioq) empty() bool {
 	return len(pq.bintree) == 0
 }