如何获得789之前所有可能的数字组合 - how to get all possible combinations of digits until 789?

how to get all possible combinations of digits until 789?

我正在尝试编写算法，以获得所有组合，并同时递增一，从而获得这个

function generate($index){
    $xxx = '';
    $flag = 0;  
    $lengtchString = strlen($index); 
    for($y = 0; $y != $lengtchString; $y++) {
        $xxx .= "$y";
    }
    while ($flag != $lengtchString ) 
    { 
        for ($i = 0; $i<$lengtchString-1; $i++) 
        {            
            $temp = $xxx[$i];  
            $xxx[$i] = $xxx[$i+1]; 
            $xxx[$i+1] = $temp;   
            echo $xxx."<br>"; 
        } 
        $flag++; 
    }
}
generate('abc');

输出为

我不仅需要得到3数字的所有组合，还需要得到所有组合。

例如，如果我写"abc"。。。我需要像一样的输出

依此类推……直到789在数字不重复的条件下。。。我真的很震惊，无法找到合适的算法。提前感谢

检查此链接PHP算法，从单个集合生成特定大小的所有组合

    <?php
    function sampling($chars, $size, $combinations = array()) {
    $charsArray = str_split($chars);
    # if it's the first iteration, the first set 
    # of combinations is the same as the set of characters
    if (empty($combinations)) {
        $combinations = $charsArray;
    }
    # we're done if we're at size 1
    if ($size == 1) {
        return $combinations;
    }
    # initialise array to put new values in
    $new_combinations = array();
    # loop through existing combinations and character set to create strings
    foreach ($combinations as $combination) {
        foreach ($charsArray as $char) {
            $new_combinations[] = $combination . $char;
        }
    }
    # call same function again for the next iteration
    return sampling($chars, $size - 1, $new_combinations);
}
// example
$output = sampling("0123456789", 3);
print "<pre>";print_r($output);

Delphi函数从给定的字符集生成所有字符组合，不包含字符重复（如果源字符串中没有重复）。

工作原理：
让我们在某个阶段进行

charset = '1203456789'
incomplete result = '12'
i goes from 3 to 10
i = 3:  charset doesn't change; recursive call executes with '123' and StartIndex = 4
i = 4: charset changes to '1204356789'; recursive call executes with '124' and StartIndex = 4; 
       charset changes back to '1203456789'
i = 5: charset changes to '12054356789'; recursive call executes with '125' and StartIndex = 4; 
       charset changes back to '1203456789'

等等…

procedure GenString(StartIndx, MaxLen: Integer; Charset, Result: string);
procedure Swap(a,b: Integer);
var
  t: Char;
begin
  t := CharSet[a];
  CharSet[a] := CharSet[b];
  CharSet[b] := t;
end;
var
  i: Integer;
begin
  if Length(Result) = MaxLen then
    Memo1.Lines.Add(Result)  // output result
  else begin
    for i := StartIndx to Length(Charset) do begin
      Swap(i, StartIndx);  //save current char to avoid further usage
      GenString(StartIndx + 1, MaxLen, Charset, Result + Charset[StartIndx]);
      Swap(i, StartIndx); //restore order
    end;
  end;
end;
usage: //Delphi strings are 1-based!
  GenString(1, 3, '0123456789', '');

输出（720个值）：