剑指Offer—27—字符串的排列

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。（输入一个字符串,长度不超过 9 (可能有字符重复),字符只包括大小写字母。）

package A27字符串的排列;
import java.io.BufferedWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
public class Solution {
public ArrayList<String> Permutation(String str) {
char[] arr = new char[str.length()];
for(int i=0;i<str.length();i++){
arr[i] = str.charAt(i);
}
ArrayList<String> list = new ArrayList<>();
test(arr, 0, str.length()-1,list);
Set<String> set = new HashSet<>();
set.addAll(list);
list.clear();
list.addAll(set);
return list;
}

public void test(char[] arr, int start, int end,ArrayList<String> list){

if (start == end) {
StringBuilder stringBuilder = new StringBuilder();
for(int i=0;i<arr.length;i++){
stringBuilder.append(arr[i]);
}
list.add(stringBuilder.toString());
}

for(int i=start;i<=end;i++){
char temp = arr[start];
arr[start] = arr[i];
arr[i] = temp;

test(arr, start+1, end,list);

temp = arr[start];
arr[start] = arr[i];
arr[i] = temp;
}
}

public static void main(String[] args) {

Solution solution = new Solution();
char[] arr = {'a','b','c'};
ArrayList<String> list = new ArrayList<>();
ArrayList<String> list2 = solution.Permutation("aa");
for (String string : list2) {

System.out.println(string);
}
}

}