剑指offer(六十一)之字符串的排列

<span style="font-family:SimSun;font-size:18px;color:#000099;">import java.util.ArrayList;
import java.util.*;
public class Solution {
public ArrayList<String> Permutation(String str) {
ArrayList<String> result = new ArrayList<String>() ;
if(str==null || str.length()==0) { return result ; }

char[] chars = str.toCharArray() ;
TreeSet<String> temp = new TreeSet<>() ;
Permutation(chars, 0, temp);
result.addAll(temp) ;
return result ;
}

public void Permutation(char[] chars, int begin, TreeSet<String> result) {
if(chars==null || chars.length==0 || begin<0 || begin>chars.length-1) { return ; }

if(begin == chars.length-1) {
result.add(String.valueOf(chars)) ;
}else {
for(int i=begin ; i<=chars.length-1 ; i++) {
swap(chars, begin, i) ;

Permutation(chars, begin+1, result);

swap(chars, begin, i) ;
}
}
}

public void swap(char[] x, int a, int b) {
char t = x[a];
x[a] = x[b];
x[b] = t;
}

}</span>