記得全排列這種寫法還是在學校圖書館看到的,回溯法中,當初理解了好久。
import java.util.*;
public class Solution {
public ArrayList<String> Permutation(String str) {
ArrayList<String> re = new ArrayList<String>();
if (str == null || str.length() == 0) {
return re;
}
HashSet<String> set = new HashSet<String>();
fun(set, str.toCharArray(), 0);
re.addAll(set);
Collections.sort(re);
return re;
}
void fun(HashSet<String> re, char[] str, int k) {
if (k == str.length) {
re.add(new String(str));
return;
}
for (int i = k; i < str.length; i++) {
swap(str, i, k);
fun(re, str, k + 1);
swap(str, i, k);
}
}
void swap(char[] str, int i, int j) {
if (i != j) {
char t = str[i];
str[i] = str[j];
str[j] = t;
}
}
}