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merge-k-sorted-lists.go
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merge-k-sorted-lists.go
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package main
/**
* Definition for singly-linked list.
* type ListNode struct {
* Val int
* Next *ListNode
* }
*/
import "container/heap"
type Item struct {
value *ListNode
priority int
index int
}
type PriorityQueue []*Item
func (pq PriorityQueue) Len() int { return len(pq) }
func (pq PriorityQueue) Less(i, j int) bool {
return pq[i].priority < pq[j].priority
}
func (pq PriorityQueue) Swap(i, j int) {
pq[i], pq[j] = pq[j], pq[i]
pq[i].index = i
pq[j].index = j
}
func (pq *PriorityQueue) Push(x interface{}) {
n := len(*pq)
item := x.(*Item)
item.index = n
*pq = append(*pq, item)
}
func (pq *PriorityQueue) Pop() interface{} {
old := *pq
n := len(old)
item := old[n-1]
item.index = -1 // for safety
*pq = old[0 : n-1]
return item
}
func mergeKLists(lists []*ListNode) *ListNode {
head := &ListNode{}
point := head
pq := make(PriorityQueue, 0)
heap.Init(&pq)
for _,l := range lists {
if l != nil {
heap.Push(&pq, &Item{
value: l,
priority: l.Val,
})
}
}
for pq.Len() > 0 {
item := heap.Pop(&pq).(*Item)
point.Next = &ListNode{
Val: item.priority,
}
point = point.Next
item.value = item.value.Next
if item.value != nil {
heap.Push(&pq, &Item{
value: item.value,
priority: item.value.Val,
})
}
}
return head.Next
}