数字和 ABC 互相转换

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<?php

function ItoA($i) {
    $i = intval($i);
    return strtoupper(chr($i+64));
}

function AtoI($s) {
    if ($s == '') {
        return 0;
    }
    $s = strtoupper($s);
    return ord($s) - 64;
}


// 数字转成 ABC
function IntToABC($i){
    $res = '';
    while (true) {
        $m = $i % 26;
        if ($m == 0) {
            $m = 26;
        }
        $res =  ItoA($m) . $res;
        $i = ($i - $m) / 26;

        if ($i <= 0) {
            break;
        }
    }
    return $res;
}

// ABC 转成数字
function ABCToInt($str) {
    if ($str == ''){
        return 0;
    }
    $res = 0;
    
    $j = 1;
    for ($i=strlen($str) -1; $i>=0; $i--){
        $cur = $str[$i];
        $res += AtoI($cur) * $j;
        $j = $j *  26;
    }
    return $res;
}

$example = [1,2,26,28,777,49,703];

foreach($example as $raw) {
    $str = IntToABC($raw);
    $i = ABCToInt($str);
    echo  "example: $raw > $str > $i " . PHP_EOL;
}

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example: 1 > A > 1
example: 2 > B > 2
example: 26 > Z > 26
example: 28 > AB > 28
example: 777 > ACW > 777
example: 49 > AW > 49
example: 703 > AAA > 703