# [PHP] 算法-字符串的全排列的PHP实现

```输入一个字符串,按字典序打印出该字符串中字符的所有排列。例如输入字符串abc,则打印出由字符a,b,c所能排列出来的所有字符串abc,acb,bac,bca,cab和cba。

1.利用递归形成递归树,达到深度优先,固定首字母的效果
2.得复位以后才能再次深度优先
3.回溯法思想
4.一张图和一个运行过程,只能慢慢体会了```
```<?php
function test(\$str,\$start,&\$res){
//递归终止条件
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();
//调用入口,从索引0开始
\$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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