A collection of basic algorithms for PHP

This article mainly introduces the basic algorithm collection of PHP, which has certain reference value. Now I share it with everyone. Friends in need can refer to it

Binary search (searching for an element in an array)

function bin_sch($array,  $low, $high, $k){   
    if ( $low <= $high){   
        $mid =  intval(($low+$high)/2 );   
        if ($array[$mid] ==  $k){   
            return $mid;   
        }elseif ( $k < $array[$mid]){   
            return  bin_sch($array, $low,  $mid-1, $k);   
        }else{   
            return  bin_sch($array, $mid+ 1, $high, $k);   
        }   
    }   
    return -1;   
}

This method is for index arrays and the value is sorted from small to large
Associative arrays are not applicable, the array sorting method is inconsistent or there is no sorting, please modify the if condition accordingly to increase the sorting Wait

Sequential search (search for an element in the array)

function  seq_sch($array, $n,  $k){   
    $array[$n] =  $k;   
    for($i=0;  $i<$n; $i++){   
        if( $array[$i]==$k){   
            break;   
        }   
    }   
    if ($i<$n){   
        return  $i;   
    }else{   
        return -1;   
    }   
}   

此方法适用于索引数组并且$n = count($array);

Simplified enhanced version

function  seq_sch($array, $k){   
    $y = $m = 'no'; 
    foreach($array as $i => $v){
        if($v == $k){  
            if($i == 'no'){$m = 'yes'}//防止key = no
            $y = $i; 
            break;   
        }   
    }   
    if ($y != 'no' || $m == 'yes'){   
        return  $y;   
    }else{   
        return -1;   
    }   
}   

此方法适用于所有一维数组

Deletion of linear tables (implemented in the array)

function delete_array_element($array , $i){  
    $len = count($array);   
    for ($j=$i; $j<$len; $j++){  
            $array[$j] = $array [$j+1];  
    }  
    array_pop ($array);  
    return $array ;  
}

$i specifies the deletion parameter position

Bubble sort (array sort)

function bubble_sort($array){  
    $count = count( $array);  
    if ($count <= 0 ) return false;  
    for($i=0 ; $i<$count; $i ++){  
        for($j=$count-1 ; $j>$i; $j--){  
            if ($array[$j] < $array [$j-1]){  
                //引用第三变量进项数组交换
                $tmp = $array[$j];  
                $array[$j] = $array[ $j-1];  
                $array [$j-1] = $tmp;  
             }  
         }  
     }  
     return $array;  
 }

Quick sort (array sort)

function quick_sort($array ) {  
    if (count($array) <= 1) return  $array;  
    $key = $array [0];  
    $left_arr  = array();  
    $right_arr = array();  
    for ($i= 1; $i<count($array ); $i++){  
        if ($array[ $i] <= $key)  
            $left_arr [] = $array[$i];  
        else  
            $right_arr[] = $array[$i];  
    }  
    $left_arr = quick_sort($left_arr);  
    $right_arr = quick_sort($right_arr);  
    return array_merge($left_arr , array($key), $right_arr);  
}

String length

function strlen ($str){  
    if ($str == '' ) return 0;  
    $count =  0;  
    while (1){  
        if ($str[$count] != NULL){  
            $count++;  
            continue;  
        }else{  
            break;  
        }  
    }  
    return $count;  
}

• while (1) 1 represents a constant expression, which will never equal 0. Therefore, the loop will continue to execute. Unless you set a break or similar statement to jump out of the loop, the loop will terminate.

• $str[count] PHP is a weakly typed language. You can use subscripts to read the corresponding parameters at the corresponding position

Intercept substring

function substr($str, $start,  $length=NULL){  
    if ($str== '' || $start>strlen($str)) return;  
    if (($length!=NULL) && ($start>0) && ($length>strlen($str)-$start)) return;  
    if (($length!=NULL) && ($start<0) && ($length>strlen($str )+$start)) return;  
    if ($length == NULL) $length = (strlen($str) - $start);  

    if ($start < 0){  
            for ($i=(strlen($str)+$start); $i<(strlen ($str)+$start+$length ); $i++) {  
                 $substr .=  $str[$i];  
            }  
    }  
    if ($length > 0){  
            for ($i= $start; $i<($start+$length); $i++) {  
                  $substr .= $str[$i];  
            }  
    }  
    if ($length < 0){  
            for ($i =$start; $i<(strlen($str)+$length); $i++) {  
                   $substr .= $str[$i ];  
            }  
    }  
    return $substr;

}

String flip

function strrev($str){  
    if ($str == '') return 0 ;  
    for ($i=(strlen($str)- 1); $i>=0; $i --){  
            $rev_str .= $str[$i ];  
    }  
    return $rev_str;  
}

String comparison

function strcmp($s1, $s2){  
    if (strlen($s1) <  strlen($s2)) return -1 ;  
    if (strlen($s1) > strlen( $s2)) return 1;  
    for ($i=0; $i<strlen($s1); $i++){  
        if ($s1[$i] == $s2[$i]){  
            continue;  
        }else{  
            return false;  
        }  
    }  
    return  0;  
}

Find string

function  strstr($str, $substr){  
    $m = strlen($str);  
    $n = strlen($substr);  
    if ($m < $n) return false ;  
    for($i=0; $i<=($m-$n+1); $i++){  
        $sub = substr($str, $i, $n);  
        if (strcmp($sub, $substr) ==  0)  return $i;  
    }  
    return false ;  
}

strcmp(

substr) String comparison method If you don’t want to use the comparison method, please add a for loop

String replacement

function str_replace($substr, $newsubstr, $str){  
    $m = strlen($str);  
    $n = strlen($substr);  
    $x = strlen($newsubstr);  
    if (strchr($str, $substr) == false) return false;
    $str_new = $str  
    for ($i=0; $i<=($m-$n+1); $i++){  
        $i = strchr($str, $substr);  
        $str = str_delete($str_new, $i, $n);  
        $str = str_insert($str_new, $i, $newstr);  
    }  
    return $str_new;  
}

• strchr() function searches for the first occurrence of a string in another string.
  This function is an alias of the strstr() function.

Insert a string

function str_insert($str, $i , $substr) {  
    for($j=0 ; $j<$i; $j++){  
            $startstr .= $str[$j];  
    }  
    for ($j=$i; $j <strlen($str); $j++){  
            $laststr .= $str[$j ];  
    }  
    $str = $startstr.$substr.$laststr;  
    return $str ;  
}

Delete a string

function str_delete($str, $i, $j){  
    for ( $c=0; $c<$i; $c++){  
        $startstr .= $str [$c];  
    }  
    for ($c=( $i+$j); $c<strlen ($str); $c++){  
        $laststr .= $str[$c];  
    }  
    $str = $startstr.$laststr;  
    return $str;  
}

Copy string

function strcpy($s1, $s2){  
    if (strlen($s1)==NULL || !isset($s2)) return;  
    for ($i=0; $i<strlen($s1); $i++){  
        $s2[] = $s1[$i];  
    }  
    return $s2;  
}

Connect string

function strcat($s1 ,$s2){  
    if (!isset($s1) || !isset( $s2)) return;  
    $newstr = $s1 ;  
    for($i=0; $i<strlen($s2); $i++){  
            $newstr .= $s2[$i];  
    }  
    return $newstr;  
}

             

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