github.com/matrixorigin/matrixone@v0.7.0/pkg/vm/engine/tae/mergesort/decimal64s/heap.go (about)

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package heap provides heap operations for any type that implements
     6  // heap.Interface. A heap is a tree with the property that each node is the
     7  // minimum-valued node in its subtree.
     8  //
     9  // The minimum element in the tree is the root, at index 0.
    10  //
    11  // A heap is a common way to implement a priority queue. To build a priority
    12  // queue, implement the Heap interface with the (negative) priority as the
    13  // ordering for the Less method, so Push adds items while Pop removes the
    14  // highest-priority item from the queue. The Examples include such an
    15  // implementation; the file example_pq_test.go has the complete source.
    16  package decimal64s
    17  
    18  // Init establishes the heap invariants required by the other routines in this package.
    19  // Init is idempotent with respect to the heap invariants
    20  // and may be called whenever the heap invariants may have been invalidated.
    21  // The complexity is Operator(n) where n = len(h).
    22  func heapInit(h heapSlice) {
    23  	// heapify
    24  	n := len(h)
    25  	for i := n/2 - 1; i >= 0; i-- {
    26  		down(h, i, n)
    27  	}
    28  }
    29  
    30  // Push pushes the element x onto the heap.
    31  // The complexity is Operator(log n) where n = len(h).
    32  func heapPush(h *heapSlice, x heapElem) {
    33  	*h = append(*h, x)
    34  	up(*h, len(*h)-1)
    35  }
    36  
    37  // Pop removes and returns the minimum element (according to Less) from the heap.
    38  // The complexity is Operator(log n) where n = len(h).
    39  // Pop is equivalent to Remove(h, 0).
    40  func heapPop(h *heapSlice) heapElem {
    41  	n := len(*h) - 1
    42  	(*h)[0], (*h)[n] = (*h)[n], (*h)[0]
    43  	down(*h, 0, n)
    44  	res := (*h)[n]
    45  	*h = (*h)[:n]
    46  	return res
    47  }
    48  
    49  func up(h heapSlice, j int) {
    50  	for {
    51  		i := (j - 1) / 2 // parent
    52  		if i == j || !h.Less(j, i) {
    53  			break
    54  		}
    55  		h.Swap(i, j)
    56  		j = i
    57  	}
    58  }
    59  
    60  func down(h heapSlice, i0, n int) bool {
    61  	i := i0
    62  	for {
    63  		j1 := 2*i + 1
    64  		if j1 >= n || j1 < 0 { // j1 < 0 after int overflow
    65  			break
    66  		}
    67  		j := j1 // left child
    68  		if j2 := j1 + 1; j2 < n && h.Less(j2, j1) {
    69  			j = j2 // = 2*i + 2  // right child
    70  		}
    71  		if !h.Less(j, i) {
    72  			break
    73  		}
    74  		h.Swap(i, j)
    75  		i = j
    76  	}
    77  	return i > i0
    78  }