使用php在循环通过capitilisations时增加字母

$low = $low2 = range('a', 'z');
$upp = $upp2 = range('A', 'Z');

$arr = array();
foreach ($low as $val)
{
  $arr[] = $val;
  foreach ($low2 as $lval)
  {
    $arr[] = $val.$lval;
  }
}

foreach ($upp as $val)
{
  $arr[] = $val;
  foreach ($upp2 as $uval)
  {
    $arr[] = $val.$uval;
  }
}

foreach ($low as $val)
{
  foreach ($upp as $uval)
  {
    $arr[] = $val.$uval;
  }
}

foreach ($upp as $val)
{
  foreach ($low as $lval)
  {
    $arr[] = $val.$lval;
  }
}

function permutations($items)
{
  empty($items)?return array():$perms = array();
  for ($i = count($items)-1; $i > 0; --$i)
  {
    $perms[] = $items[0].$items[$i];
  }
  return array_merge($perms, permutations(array_slice($items,1)));
}

$lowercase

$uppercase

<?php

    $lowercase = array(97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122);

    $uppercase = array(65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90);

    $i = 0;
    for($i; $i < 26; $i++) {
        echo chr($lowercase[$i]) . ", ";
        echo chr($uppercase[$i]) . ", ";
    }

    $i = 0;
    for($i; $i < 26; $i++) {
        echo chr($lowercase[$i]);
        echo chr($lowercase[$i]);
        echo ", ";
        echo chr($uppercase[$i]);
        echo chr($lowercase[$i]);
        echo ", ";
        echo chr($lowercase[$i]);
        echo chr($uppercase[$i]);
        echo ", ";
        echo chr($uppercase[$i]);
        echo chr($uppercase[$i]);
        echo ", ";
    }

?>

a, A, b, B, c, C, d, D, e, E, f, F, g, G, h, H, i, I, j, J, k, K, l, L, m, M, n, N, o, O, p, P, q, Q, r, R, s, S, t, T, u, U, v, V, w, W, x, X, y, Y, z, Z, aa, Aa, aA, AA, bb, Bb, bB, BB, cc, Cc, cC, CC, dd, Dd, dD, DD, ee, Ee, eE, EE, ff, Ff, fF, FF, gg, Gg, gG, GG, hh, Hh, hH, HH, ii, Ii, iI, II, jj, Jj, jJ, JJ, kk, Kk, kK, KK, ll, Ll, lL, LL, mm, Mm, mM, MM, nn, Nn, nN, NN, oo, Oo, oO, OO, pp, Pp, pP, PP, qq, Qq, qQ, QQ, rr, Rr, rR, RR, ss, Ss, sS, SS, tt, Tt, tT, TT, uu, Uu, uU, UU, vv, Vv, vV, VV, ww, Ww, wW, WW, xx, Xx, xX, XX, yy, Yy, yY, YY, zz, Zz, zZ, ZZ,

e.g.
  00 = aa
  01 = aA
  10 = Aa
  11 = AA

(actually I have iterated bits from lowest to highest rank to get the order to match your example)

$maxwidth = 3;
for ( $width = 1; $width <= $maxwidth; $width++ ) {
    for ( $letter = ord('a'); $letter <= ord('z'); $letter++ ) {
        for ( $num = 0; $num < pow(2,$width); $num++ ) {
            for ( $bit = 0; $bit < $width; $bit++ ) {
                print ($num & pow(2, $bit)) ? strtoupper(chr($letter)) : chr($letter);  
            }
            print ','; 
        }
    }
    print "n";
}

$a++

$single_set = array(); // array holding single-character sequence
$double_set = array(); // array holding double-character sequence

for ($v1 = 'a', $v2 = 'A'; $v1 !== 'aa'; $v1++, $v2++) {
    $single_set[] = $v1;
    $single_set[] = $v2;
    $double_set[] = $v1 . $v1;
    $double_set[] = $v1 . $v2;
    $double_set[] = $v2 . $v1;
    $double_set[] = $v2 . $v2;
    }

$set = $single_set + $double_set; // combined array sequence