Generate a 4-character string, including abcdefg. How can we get all the combinations?

How to implement the Program to store all the possibilities in an array. We can repeat aaaa. It is best to implement PHP to store all the possibilities in an array and how to implement the program.
It can be repeated, such as aaaa. It is best to implement it in PHP.

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How to implement the Program to store all the possibilities in an array.
It can be repeated, such as aaaa. It is best to implement it in PHP.

Python

import itertoolsprint list(itertools.permutations(["a","b","c","d","e","f"，"g"],4))

Php

You can try this:

Http://www.honglei.net /? P = 167

Do you want to consider the existence of aaaa? In fact, we can consider encoding them. Suppose abcdefg corresponds to 0123456 respectively, then all the situations are:

0000 (that is, 0 )~ 6666 all numbersLa.

Ps: in hexadecimal notation

Code directly, four for loops, simple, violent, and fast

function dfs($pre, $chars, $arr, $lenArr) {    if(!empty($pre) && in_array(strlen($pre), $lenArr)){ $arr[] = $pre; }    if(!empty($chars)) {        foreach ($chars as $char) {            $tempChars = array();            foreach ($chars as $c) {                if ($c !== $char) { $tempChars[] = $c; }            }            $arr = $this->dfs($pre.$char, $tempChars, $arr, $lenArr);        }    }    return $arr;}function get_combine() {    $chars = array('a', 'b', 'c', 'd', 'e', 'f', 'g');    $combineArray = array();    $combineArray = $this->dfs('', $chars, $combineArray, array(4));    echo count($combineArray).'
';    var_dump($combineArray);}