How to improve efficiency by searching array elements through PHP

1.php in_array method description

php finds whether an array element exists. Generally, the in_array method is used.

bool in_array ( mixed $needle , array $haystack [, bool $strict = FALSE ] )

Parameter description:
needle
The value to be searched. If needle is a string, the comparison is case-sensitive.

haystack
Array used for comparison

strict
If the value of the third parameter strict is TRUE, then in_array( ) The function also checks whether the type of needle is the same as that in haystack

Return value
If needle is found, it returns TRUE, otherwise it returns FALSE .

2.Efficiency of finding elements in in_array

When the compared array haystack is large, the efficiency of in_array will be very low

Example: There are 100,000 in_array pairs The array of elements is compared 1000 times

<?php $arr = array();// 创建10万个元素的数组for($i=0; $i<100000; $i++){    $arr[] = $i;
}// 记录开始时间$starttime = getMicrotime();// 随机创建1000个数字使用in_array比较for($j=0; $j<1000; $j++){    $str = mt_rand(1,99999);
    in_array($str, $arr);
}// 记录结束时间$endtime = getMicrotime();echo &#39;run time:&#39;.(float)(($endtime-$starttime)*1000).&#39;ms<br>';/**
 * 获取microtime
 * @return float
 */function getMicrotime(){
    list($usec, $sec) = explode(' ', microtime());    return (float)$usec + (float)$sec;
}?>

run time:2003.6449432373ms

Use in_array to determine whether the element exists, in 100,000 Comparing an array of elements 1000 times, the running time takes about 2 seconds

3. Method to improve the efficiency of finding elements

We can use array_flip## first #Exchange key values, and then use the isset method to determine whether the element exists, which can improve efficiency.

Example: Use array_flip to perform key-value exchange first, then use the isset method to judge, and compare 1000 times in an array of 100,000 elements

<?php $arr = array();// 创建10万个元素的数组for($i=0; $i<100000; $i++){    $arr[] = $i;
}// 键值互换$arr = array_flip($arr);// 记录开始时间$starttime = getMicrotime();// 随机创建1000个数字使用isset比较for($j=0; $j<1000; $j++){    $str = mt_rand(1,99999);    isset($arr[$str]);
}// 记录结束时间$endtime = getMicrotime();echo &#39;run time:&#39;.(float)(($endtime-$starttime)*1000).&#39;ms<br>';/**
 * 获取microtime
 * @return float
 */function getMicrotime(){
    list($usec, $sec) = explode(' ', microtime());    return (float)$usec + (float)$sec;
}?>

run time:

1.2781620025635ms

Use

array_flip and isset to determine whether an element exists. Compare 1000 times in an array of 100,000 elements. The running time is About 1.2 milliseconds
Therefore, for comparison of large arrays, using the array_flip and isset methods will be more efficient than in_array Much higher.

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