Refactor prio queue

Author: korthaj

heap.go

@@ -0,0 +1,67 @@
+package graph
+
+import (
+	"container/heap"
+)
+
+type prioQueue struct {
+	heap  []int // vertices in heap order
+	index []int // index of each vertex in the heap
+	cost  []int64
+}
+
+func emptyQueue(cost []int64) *prioQueue {
+	return &prioQueue{
+		index: make([]int, len(cost)),
+		cost:  cost,
+	}
+}
+
+func newQueue(cost []int64) *prioQueue {
+	n := len(cost)
+	h := &prioQueue{
+		heap:  make([]int, n),
+		index: make([]int, n),
+		cost:  cost,
+	}
+	for i := range h.heap {
+		h.heap[i] = i
+		h.index[i] = i
+	}
+	return h
+}
+
+func (m *prioQueue) Len() int { return len(m.heap) }
+
+func (m *prioQueue) Less(i, j int) bool {
+	return m.cost[m.heap[i]] < m.cost[m.heap[j]]
+}
+
+func (m *prioQueue) Swap(i, j int) {
+	m.heap[i], m.heap[j] = m.heap[j], m.heap[i]
+	m.index[m.heap[i]] = i
+	m.index[m.heap[j]] = j
+}
+
+func (pq *prioQueue) Push(x interface{}) {
+	n := len(pq.heap)
+	v := x.(int)
+	pq.heap = append(pq.heap, v)
+	pq.index[v] = n
+}
+
+func (m *prioQueue) Pop() interface{} {
+	n := len(m.heap) - 1
+	v := m.heap[n]
+	m.index[v] = -1
+	m.heap = m.heap[:n]
+	return v
+}
+
+func (m *prioQueue) Update(v int) {
+	heap.Fix(m, m.index[v])
+}
+
+func (m *prioQueue) Contains(v int) bool {
+	return m.index[v] >= 0
+}