1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
|
// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
namespace vespalib {
/**
* The LeftHeap is used to maintain a heap stored in the start (LEFT
* side) of an array. The input to push and the output from pop is the
* last element in the range defined by the parameters. This means
* that a LeftHeap grows and shrinks at its right side. To access the
* best (first) item in the heap before popping it, you need to use
* the front function, since the placement of the best item prior to
* popping it can vary with different implementations.
*
* A LeftHeap works the same way as the heap in the standard library
* with the exception of having the comparator inverted. This means
* that when you pop the heap, you will get the first element on the
* heap, not the last. This marks the death of heapsort and the
* resurrection of heap as a useful data structure.
**/
struct LeftHeap {
static void require_left_heap() {} // for compile-time checks
template <typename T> static T &front(T *begin, T *) { return *begin; }
template <typename T, typename C> static void push(T *begin, T *end, C cmp);
template <typename T, typename C> static void pop(T *begin, T *end, C cmp);
template <typename T, typename C> static void adjust(T *begin, T *end, C cmp);
};
/**
* The RightHeap is used to maintain a heap stored in the end (RIGHT
* side) of an array. The input to push and the output from pop is the
* first element in the range defined by the parameters. This means
* that a RightHeap grows and shrinks at its left side. The RightHeap
* is generally harder to work with compared to the LeftHeap and is
* only useful when you want to put heaps in both sides of an
* array. This can be useful when there is a fixed number of elements
* that has different priority order based on some partitioning
* criteria that change over time.
**/
struct RightHeap {
static void require_right_heap() {} // for compile-time checks
template <typename T> static T &front(T *, T *end) { return *(end - 1); }
template <typename T, typename C> static void push(T *begin, T *end, C cmp);
template <typename T, typename C> static void pop(T *begin, T *end, C cmp);
template <typename T, typename C> static void adjust(T *begin, T *end, C cmp);
};
/**
* A LeftArrayHeap is a sorted array that has the same interface as
* the LeftHeap. This alternative could give better performance with
* few elements.
**/
struct LeftArrayHeap {
static void require_left_heap() {} // for compile-time checks
template <typename T> static T &front(T *, T *end) { return *(end - 1); }
template <typename T, typename C> static void push(T *begin, T *end, C cmp);
template <typename T, typename C> static void pop(T *, T *, C) {}
template <typename T, typename C> static void adjust(T *begin, T *end, C cmp) {
push(begin, end, cmp);
}
};
/**
* A RightArrayHeap is a sorted array that has the same interface as
* the RightHeap. This alternative could give better performance with
* few elements.
**/
struct RightArrayHeap {
static void require_right_heap() {} // for compile-time checks
template <typename T> static T &front(T *begin, T *) { return *begin; }
template <typename T, typename C> static void push(T *begin, T *end, C cmp);
template <typename T, typename C> static void pop(T *, T *, C) {}
template <typename T, typename C> static void adjust(T *begin, T *end, C cmp) {
push(begin, end, cmp);
}
};
/**
* A LeftStdHeap adapts the heap implementation in the standard
* library to the LeftHeap interface by inverting the comparator and
* restricting the iterator types.
**/
struct LeftStdHeap {
static void require_left_heap() {} // for compile-time checks
template <typename T> static T &front(T *begin, T *) { return *begin; }
template <typename T, typename C> static void push(T *begin, T *end, C cmp);
template <typename T, typename C> static void pop(T *begin, T *end, C cmp);
template <typename T, typename C> static void adjust(T *begin, T *end, C cmp);
};
} // namespace vespalib
#include "left_right_heap.hpp"
|
