字符串的排列java实现

import java.util.ArrayList;
import java.util.Stack;
import java.util.TreeSet;
public class Solution {
public ArrayList<String> Permutation(String str) {
TreeSet<String> tree = new TreeSet<String>();
Stack<String[]> stack = new Stack<String[]>();
ArrayList<String> results = new ArrayList<String>();
stack.push(new String[]{str,""});
do{
String[] popStrs = stack.pop();
String oldStr = popStrs[1];
String statckStr = popStrs[0];
for(int i =statckStr.length()-1;i>=0;i--){
String[] strs = new String[]{statckStr.substring(0,i)+statckStr.substring(i+1),oldStr+statckStr.substring(i,i+1)};
if(strs[0].length()==0){
tree.add(strs[1]);
}else{
stack.push(strs);
}
}
}while(!stack.isEmpty());
for(String s : tree)
results.add(s);
return results;
}
}