[算法 笔记]大根堆

View Code

  1 /**

  2  * 大根堆。从STL中获得。

  3  */

  4 

  5 #include <iostream>

  6 #include <ctime>

  7 #include <cmath>

  8 #include <cstdlib>

  9 

 10 using namespace std;

 11 

 12 void _push_heap(int *start, int holeIndex, int topIndex, int value)

 13 {

 14     int parent = (holeIndex - 1) / 2;

 15     while (holeIndex > topIndex  && *(start + parent) < value)

 16     {

 17         *(start + holeIndex) = *(start + parent);

 18         holeIndex = parent;

 19         parent = (holeIndex - 1) / 2;

 20     }

 21     *(start + holeIndex) = value;

 22 }

 23 

 24 void adjust_heap(int *start, int holeIndex, int length, int value)

 25 {

 26     int topIndex = holeIndex;

 27     int secondChild = 2 * holeIndex + 2;

 28 

 29     while (secondChild < length)

 30     {

 31         // 大根堆的调整

 32         if (*(start + secondChild) < *(start + secondChild - 1))

 33             secondChild--;

 34         *(start + holeIndex) = *(start + secondChild);

 35         holeIndex = secondChild;

 36         secondChild = 2 * holeIndex + 2;

 37     }

 38 

 39     if (secondChild == length) {

 40         *(start + holeIndex) = *(start + secondChild - 1);

 41         holeIndex = secondChild - 1;

 42     }

 43 

 44     _push_heap(start, holeIndex, topIndex, value);

 45 }

 46 

 47 

 48 void push_heap(int *start, int *end)

 49 {

 50     _push_heap(start, start - end - 1, 0, *(end - 1));

 51 }

 52 

 53 int pop_heap(int *start, int *end)

 54 {

 55     int result = *start;

 56     adjust_heap(start, 0, end - start, *(end - 1));

 57 

 58     return result;

 59 }

 60 

 61 void make_heap(int *start, int *end)

 62 {

 63     if (end - start < 2) return ;

 64     int length = end - start;

 65     int parent = (length - 2) / 2;

 66 

 67     while (true) {

 68         adjust_heap(start, parent, length, *(start + parent));

 69         if (parent == 0) return;

 70         parent--;

 71     }

 72 }

 73 

 74 void sort_heap(int *start, int *end)

 75 {

 76     while (end - start > 1)

 77         cout << pop_heap(start, end--) << "\t" ;

 78 }

 79 

 80 int test(void)

 81 {

 82     enum {maxsize = 500};

 83     int a[maxsize], i;

 84     srand((int)time(0));

 85 

 86     cout << "test array: " << endl;

 87     for (i = 0; i < maxsize; i++)

 88     {

 89         a[i] = rand();

 90         cout << a[i] << "\t";

 91     }

 92     int size = sizeof(a) / sizeof(int);

 93     cout << endl << endl;

 94     cout << "result: " << endl;

 95 

 96     make_heap(a, a + size);

 97     sort_heap(a, a + size);

 98 

 99     return 0;

100 }

101 

102 int main()

103 {

104     test();

105 

106     return 0;

107 }