Summary of various methods of finding array elements in PHP

Summary of various methods of finding array elements in PHP_PHP Tutorial

WBOY

Release： 2016-07-13 16:57:10

Original

1185 people have browsed it

Data query in php can be classified into one-dimensional array search and multi-dimensional array search. If it is a simple one-dimensional array, we can directly use in_array, array_search and traversal to instantiate it. If it is a multi-dimensional array, we need to use other methods. .

For a one-dimensional array we can operate as follows

in_array 'Function searches for a given value in an array. in_array(value,array,type)type optional. If this parameter is set to true, it is checked whether the type of the searched data and the value of the array are the same.

array_key_exists 'array_key_exists() function determines whether the specified key exists in an array. If the key exists, it returns true, otherwise it returns false. array_key_exists(key,array)

array_search 'array_search() function is the same as in_array(), searching for a key value in an array. If the value is found, the key of the matching element is returned. If not found, returns false. array_search(value,array,strict)

From this point of view, when the amount of data is not large, such as less than 1000, any search method can be used, and it will not become a bottleneck;
When the amount of data is relatively large, array_key_exists is more appropriate.
Of course, the memory occupied by array_key_exists here is relatively large. According to calculations

Binary method to find whether an array contains a certain element, compatible with forward and reverse order, code implementation:

The code is as follows

Copy code

代码如下

复制代码

$searchValue = (int)$_GET['key'];

function search(array $array, $value)
{
$max = count($array)-1;
$min = 0;
$isAscSort = $array[$min] < $array[$max];

while (TRUE) {
$sum = $min+$max;
$midKey = (int)($sum%2 == 1 ? ceil($sum/2) : $sum/2);

if ($max < $min) {
return -1;
} else if ($value == $array[$midKey]) {
return 1;
} else if ($value > $array[$midKey]) {
$isAscSort ? $min = $midKey+1 : $max = $midKey-1;
} else if ($value < $array[$midKey]) {
$isAscSort ? $max = $midKey-1 : $min = $midKey+1;
}
}
}

$array = array(
'4', '5', '7', '8', '9', '10', '11', '12'
);
// 正序
echo search($array, $searchValue);

// 逆序
rsort($array);
echo search($array, $searchValue);

<🎜>$searchValue = (int)$_GET['key'];<🎜> <🎜>function search(array $array, $value)<🎜> {<🎜> $max = count($array)-1;<🎜> $min = 0;<🎜> $isAscSort = $array[$min] < $array[$max];<🎜> <🎜>while (TRUE) {<🎜> $sum = $min+$max;<🎜> $midKey = (int)($sum%2 == 1 ? ceil($sum/2) : $sum/2);<🎜> <🎜>if ($max < $min) {<🎜> return -1;<🎜> } else if ($value == $array[$midKey]) {<🎜> return 1;<🎜> } else if ($value > $array[$midKey]) { $isAscSort ? $min = $midKey+1 : $max = $midKey-1; } else if ($value < $array[$midKey]) {<🎜> $isAscSort ? $max = $midKey-1 : $min = $midKey+1;<🎜> }<🎜> }<🎜> }<🎜> <🎜>$array = array(<🎜> '4', '5', '7', '8', '9', '10', '11', '12'<🎜> );<🎜> // Positive sequence<🎜> echo search($array, $searchValue);<🎜> <🎜>//reverse order<🎜> rsort($array);<🎜> echo search($array, $searchValue);<🎜>

Example 2

PHP Find the i-th smallest element in an array

The code is as follows

Copy code

#Randomly select the i-th smallest number and use random quick sort to achieve

#Exchange elements
Function swap(&$arr, $i, $j) {
           $temp = $arr[$i];
           $arr[$i] = $arr[$j];
           $arr[$j] = $temp;
}

#Randomly divided
Function randomized_partition(&$arr, $begin, $end) {
           $rand_inx = rand($begin, $end);
            swap($arr, $begin, $rand_inx);
            return partition($arr, $begin, $end);
}

#Division
Function partition(&$arr, $begin, $end) {
#Use the first element as the central element
            $pivot = $begin;
           $low = $begin;
           $high = $end;

while ($low < $high) {
                  while ($low < $high && $arr[$low] <= $arr[$pivot]) {
                     $low++;
             }

                    while ($low < $high && $arr[$high] >= $arr[$pivot]) {
$high--;
             }

                 swap($arr, $low, $high);
         }

           #Exchange hub element
If ($arr[$pivot] < $arr[$low]) {
                 $low--;
         }
            swap($arr, $pivot, $low);
          return $low;
}

#Quick sort, not used here
Function quick_sort(&$arr, $begin, $end) {
            $q = randomized_partition($arr, $begin, $end);
If ($q > $begin) {
                quick_sort($arr, $begin, $q - 1);
         }
              if ($q < $end) {
                quick_sort($arr, $q + 1, $end);
         }
}

#Select the i-th smallest number
Function randomized_select(&$arr, $begin, $end, $i) {
             if ($begin == $end) {
                 return $arr[$begin];
         }

            $q = randomized_partition($arr, $begin, $end);
            $k = $q - $begin + 1; #k represents the number of elements less than or equal to q

               if ($k == $i) { #If k=i, it means that q is the coordinate of the i-th smallest element
                 return $arr[$q];
                                                                                                                  {                  return randomized_select($arr, $begin, $q - 1, $i);
             } else { #The i-th smallest element is located on the right side of q. At this time, find the i-kth smallest element on the right
                  return randomized_select($arr, $q + 1, $end, $i - $k);
         }
}

$arr = array(1, 5, 3, 7, 0, 0, 8, 4, 2, 9, 11);
$t = randomized_select($arr, 0, count($arr) - 1, 8);
Print_r("The 8th minimum element: {$t}");
echo "
";
Quick_sort($arr, 0, count($arr) - 1);
Print_r($arr);
?>