[PHP学习] 如何实现字符串的全排列-php教程

输出一个字符串,按字典序打印出该字符串中字符的一切陈列。

例如，输出字符串abc,则打印出由字符a,b,c所能陈列进去的一切字符串abc,acb,bac,bca,cab以及cba。
思绪:
1.行使递归构成递归树,达到深度优先,固定首字母的成果

2.患上复位当前能力再次深度优先

3.回溯法思维

4.一张图以及一个运转进程,只能缓缓领会了

<?phpfunction test($str,$start,&$res){        //递归终止前提
        if($start==strlen($str)){                $res[]=$str;                return;
        }   
        //  
        for($i=$start;$i<strlen($str);++$i){                if($i==$start || $str{$i}!=$str{$start}){
                        swap($str,$i,$start);var_dump($str.'==='.$start);var_dump($res);sleep(1);
                        test($str,$start+1,$res);
                        swap($str,$i,$start);
                }   
    
        }   
        return $res;
}function swap(&$str,$a,$b){        
if(!is_string($str)) return;        
$t=$str{$a};        
$str{$a}=$str{$b};        
$str{$b}=$t;
}$str="abc";$res=array();//挪用入口,从索引0开端
$res=test($str,0,$res);
var_dump($res);

string(7) "abc===0"array(0) {
}string(7) "abc===1"array(0) {
}string(7) "abc===2"array(0) {
}string(7) "acb===1"array(1) {
  [0]=>  string(3) "abc"}string(7) "acb===2"array(1) {
  [0]=>  string(3) "abc"}string(7) "bac===0"array(2) {
  [0]=>  string(3) "abc"
  [1]=>  string(3) "acb"}string(7) "bac===1"array(2) {
  [0]=>  string(3) "abc"
  [1]=>  string(3) "acb"}string(7) "bac===2"array(2) {
  [0]=>  string(3) "abc"
  [1]=>  string(3) "acb"}string(7) "bca===1"array(3) {
  [0]=>  string(3) "abc"
  [1]=>  string(3) "acb"
  [2]=>  string(3) "bac"}string(7) "bca===2"array(3) {
  [0]=>  string(3) "abc"
  [1]=>  string(3) "acb"
  [2]=>  string(3) "bac"}string(7) "cba===0"array(4) {
  [0]=>  string(3) "abc"
  [1]=>  string(3) "acb"
  [2]=>  string(3) "bac"
  [3]=>  string(3) "bca"}string(7) "cba===1"array(4) {
  [0]=>  string(3) "abc"
  [1]=>  string(3) "acb"
  [2]=>  string(3) "bac"
  [3]=>  string(3) "bca"}string(7) "cba===2"array(4) {
  [0]=>  string(3) "abc"
  [1]=>  string(3) "acb"
  [2]=>  string(3) "bac"
  [3]=>  string(3) "bca"}string(7) "cab===1"array(5) {
  [0]=>  string(3) "abc"
  [1]=>  string(3) "acb"
  [2]=>  string(3) "bac"
  [3]=>  string(3) "bca"
  [4]=>  string(3) "cba"}string(7) "cab===2"array(5) {
  [0]=>  string(3) "abc"
  [1]=>  string(3) "acb"
  [2]=>  string(3) "bac"
  [3]=>  string(3) "bca"
  [4]=>  string(3) "cba"}array(6) {
  [0]=>  string(3) "abc"
  [1]=>  string(3) "acb"
  [2]=>  string(3) "bac"
  [3]=>  string(3) "bca"
  [4]=>  string(3) "cba"
  [5]=>  string(3) "cab"}

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