字符串的排列
字符串的排列
http://www.nowcoder.com/practice/fe6b651b66ae47d7acce78ffdd9a96c7
Java的实现配合上牛客网无解的题目模板（返回值ArrayList<String>）
import java.util.*;
import java.util.stream.*;
public class Solution {
public ArrayList<String> Permutation(String str) {
ArrayList<String> ret = new ArrayList<>();
if (str == null || str.length() == 0) {
return ret;
}
perm(0, str.toCharArray(), ret);
List<String> res = ret.stream().distinct().sorted().collect(Collectors.toList());
return new ArrayList<>(res);
}
private void perm(int pos, char[] a, ArrayList<String> ret) {
if (pos + 1 == a.length) {
ret.add(new String(a));
return;
}
for (int i = pos; i < a.length; ++i) {
char tmp = a[i];
a[i] = a[pos];
a[pos] = tmp;
perm(pos + 1, a, ret);
tmp = a[i];
a[i] = a[pos];
a[pos] = tmp;
}
}
} 
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