字符串的排列

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。 

import java.util.*;
public class Solution {
    public ArrayList<String> Permutation(String str) {
    	ArrayList<String> list = new ArrayList<>();
        if (str == null || "".equals(str)) return list;
        char[] chars = str.toCharArray();
        Arrays.sort(chars);
       	list.add(charToString(chars));
        while (getNextPermutation(chars)) {
            list.add(charToString(chars));
        }
        return list;
    }
    
    public String charToString(char[] chars) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < chars.length; i++) {
            sb.append(chars[i]);
        }
        return sb.toString();
    }
    
    public boolean getNextPermutation(char[] chars) {
        if (chars.length == 1) {
            return false;
        }
        int i = chars.length - 1;
        for (;;) {
            int ii = i;
            i--;
            if (chars[i] < chars[ii]) {
                int j = chars.length ;
                while (chars[i] >= chars[--j]) ;
                char tmp = chars[i];
                chars[i] = chars[j];
                chars[j] = tmp;
                reverse(chars, ii, chars.length - 1);
                return true;
            }
            if (i == 0) {
                reverse(chars, 0, chars.length - 1);
                return false;
            }
        }
    }
    
    public void reverse(char[] chars, int s, int e) {
        for (int i = s, j = e; i < j ; i++, j--) {
            char tmp = chars[i];
            chars[i] = chars[j];
            chars[j] = tmp;
        }
    }
}