本文实例讲述了PHP实现bitmap位图排序求交集的方法。分享给大家供大家参考，具体如下：
初始化一串全为0的二进制;
现有一串无序的整数数组;
如果整数x在这个整数数组当中,就将二进制串的第x位置为1;
然后顺序读取这个二进制串,并将为1的位转换成整数,顺序存放到新的集合中,就是排好序的了
排序代码:
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function sort()
{
// var_dump(PHP_INT_MAX, PHP_INT_SIZE);
// int 9223372036854775807
// int 8
$bitmap = array_fill(0, 50, 0); //申请一个整形数组, 50个元素, 初始化为整数0
$int_bit_size = PHP_INT_SIZE * 8; //$bitmap中每个整形的二进制位数 (本例中int = 8*8 = 64bit; $bitmap数组一共50*64 = 3200个bit位),也就是说能为最大值小于等于3200的整数集合排序
$a = array(1,4,3,50,34,60,100,88,200,150,300); //定义一个乱序的数组
//扫描$a中的每一个数, 将其转换为 x*64 + y
foreach ($a as $k => $v) {
$shang = $v / $int_bit_size;
$yushu = $v % $int_bit_size;
$offset = 1 << $yushu;
$bitmap[$shang] = $bitmap[$shang] | $offset;//将bit位置为1
}
//将$bitmap中的bit位依次还原为整数输出,即可得到排序后的数组
$b = array();
foreach ($bitmap as $k => $v) {
for ($i = 0; $i < $int_bit_size; $i++) {
$tmp = 1 << $i;
$flag = $tmp & $bitmap[$k];
// $b[] = $flag ? $k * $int_bit_size + $i : false;
if ($flag) {
$b[] = $k * $int_bit_size + $i;
}
}
}
var_dump($b);exit;
}
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浏览器输出:
array
0 => int 1
1 => int 3
2 => int 4
3 => int 34
4 => int 50
5 => int 60
6 => int 88
7 => int 100
8 => int 150
9 => int 200
10 => int 300
求交集代码:
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public function sort($a = array())
{
// var_dump(PHP_INT_MAX, PHP_INT_SIZE);
// int 9223372036854775807
// int 8
$bitmap = array_fill(0, 50, 0); //申请一个整形数组, 50个元素, 初始化为整数0
$int_bit_size = PHP_INT_SIZE * 8; //$bitmap中每个整形的二进制位数 (本例中int = 8*8 = 64bit; $bitmap数组一共50*64 = 3200个bit位)
// $a = array(1,4,3,50,34,60,100,88,200,150,300); //定一个乱序的数组
//扫描$a中的每一个数, 将其转换为 x*64 + y
foreach ($a as $k => $v) {
$shang = $v / $int_bit_size;
$yushu = $v % $int_bit_size;
$offset = 1 << $yushu;
$bitmap[$shang] = $bitmap[$shang] | $offset;//将bit位置为1
}
return $bitmap;
}
public function intersect()
{
$int_bit_size = PHP_INT_SIZE * 8;
$a = array(1,4,3,50,34,60,100,88,200,150,300);
$b = array(1,5,3,50,34,55,100,87,222,150,300);
$bit_a = $this->sort($a);
$bit_b = $this->sort($b);
$c = array();
foreach ($bit_a as $k => $v) {
$c[$k] = $bit_a[$k] & $bit_b[$k]; //二进制 & 计算求交集
}
$d = array();
foreach ($c as $k => $v) {
for ($i = 0; $i < $int_bit_size; $i++) {
$tmp = 1 << $i;
$flag = $tmp & $c[$k];
// $b[] = $flag ? $k * $int_bit_size + $i : false;
if ($flag) {
$d[] = $k * $int_bit_size + $i;
}
}
}
var_dump($d);exit;
}
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浏览器输出:
array
0 => int 1
1 => int 3
2 => int 34
3 => int 50
4 => int 100
5 => int 150
6 => int 300
希望本文所述对大家PHP程序设计有所帮助。