面试题38：字符串的排列

题目：输入一个字符串，打印出该字符串中字符的所有排列。
思路：使用递归来做，
解决方案：
···
public class Question38 {
public static void permutation(char[] str){
if (str == null) return;
permutation(str, 0);

}
private static void permutation(char[] str,int begin){
    if (begin == str.length - 1) {
        String result = new String(str);
        System.out.println(result);
    }else {
        for (int i=0; i<str.length; i++){
            swap(str, begin, i);
            permutation(str, begin+1);
            swap(str, begin, i);
        }
    }
}
private static void swap(char[] str, int index1, int index2){
    char tmp = str[index1];
    str[index1] = str[index2];
    str[index2] = tmp;
}

public static void main(String[] args) {
    String str = "abc";
    char[] arr = str.toCharArray();
    permutation(arr);
}

}
···