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一、intheap的堆排序接口

// An IntHeap is a min-heap of ints.
type IntHeap []int

func (h IntHeap) Len() int           { return len(h) }
func (h IntHeap) Less(i, j int) bool { return h[i] < h[j] }
func (h IntHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }

func (h *IntHeap) Push(x any) {
	// Push and Pop use pointer receivers because they modify the slice's length,
	// not just its contents.
	*h = append(*h, x.(int))
}

func (h *IntHeap) Pop() any {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

二、节点的堆排序实现

// An Item is something we manage in a priority queue.
type Item struct {
	value    string // The value of the item; arbitrary.
	priority int    // The priority of the item in the queue.
	// The index is needed by update and is maintained by the heap.Interface methods.
	index int // The index of the item in the heap.
}

// A PriorityQueue implements heap.Interface and holds Items.
type PriorityQueue []*Item

func (pq PriorityQueue) Len() int { return len(pq) }

func (pq PriorityQueue) Less(i, j int) bool {
	// We want Pop to give us the highest, not lowest, priority so we use greater than here.
	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 any) {
	n := len(*pq)
	item := x.(*Item)
	item.index = n
	*pq = append(*pq, item)
}

func (pq *PriorityQueue) Pop() any {
	old := *pq
	n := len(old)
	item := old[n-1]
	old[n-1] = nil  // avoid memory leak
	item.index = -1 // for safety
	*pq = old[0 : n-1]
	return item
}

三、leetcode 23. 合并 K 个升序链表

23. 合并 K 个升序链表

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func mergeKLists(lists []*ListNode) *ListNode {
	if len(lists) == 0 {
		return nil
	}
	dummy := &ListNode{
		Val:  -1,
		Next: nil,
	}
	p := dummy
	pq := &PriorityQueue{}
	for _, h := range lists {
		if h != nil {
			heap.Push(pq, h)
		}
	}
	for pq.Len() != 0 {
		node := heap.Pop(pq).(*ListNode)
		p.Next = node
		if node.Next != nil {
			heap.Push(pq, node.Next)
		}
		p = p.Next
	}
	return dummy.Next

}

// A PriorityQueue implements heap.Interface and holds Items.
type PriorityQueue []*ListNode

func (pq PriorityQueue) Len() int { return len(pq) }

func (pq PriorityQueue) Less(i, j int) bool {
	// We want Pop to give us the highest, not lowest, priority so we use greater than here.
	return pq[i].Val < pq[j].Val
}

func (pq PriorityQueue) Swap(i, j int) {
	pq[i], pq[j] = pq[j], pq[i]
}

func (pq *PriorityQueue) Push(x any) {
	*pq = append(*pq, x.(*ListNode))
}

func (pq *PriorityQueue) Pop() any {
	old := *pq
	n := len(old)
	item := old[n-1]
	old[n-1] = nil // avoid memory leak
	*pq = old[0 : n-1]
	return item
}