http://d.hatena.ne.jp/JunichiIto/20111102/1320253815 の"問題1: Excel列名変換問題"

alpha2num.php

#!/usr/bin/env php
<?php

function main($str=null){
    if(!ctype_alpha($str)){
        return;
    }
        
    $chars = str_split($str);
    $chars = array_reverse($chars);
    $range = range(0, count($chars)-1);
    $numbers = array_map(function($s, $i){ 
            $code = ord($s)-64;
            if($code > 0 || $code < 27){
                return pow(26, $i) * $code;
            }
        }, $chars, $range);

    return array_sum($numbers);
}

function test(){
    assert(main('A') === 1);
    assert(main('B') === 2);
    assert(main('Z') === 26);
    assert(main('AA') === 27);
    assert(main('XFD') === 16384);


    assert(main() === null);
    assert(main(0) === null);
    assert(main('0') === null);
    assert(main('') === null);
    assert(main(false) === null);
    assert(main("ほげ") === null);
}


if(count($argv) !== 2){
    echo 'Usage: '.$argv[0].' ARG', "\n";
    exit(0);
}

$stdin = trim($argv[1]);
if($stdin){
    echo main($stdin), "\n";
}

exit(0);