1，这个是自己写的。一直LTE。
public static ArrayList<String> getPerms(String str) {
if (str == null) {
return null;
}
ArrayList<String> permutations = new ArrayList<String>();
if (str.length() == 0) { // base case
permutations.add("");
return permutations;
}
char first = str.charAt(0); // get the first character
String remainder = str.substring(1); // remove the first character
ArrayList<String> words = getPerms(remainder);
for (String word : words) {
for (int j = 0; j <= word.length(); j++) {
String s = insertCharAt(word, first, j);
permutations.add(s);
}
}
return permutations;
}
public static String insertCharAt(String word, char c, int i) {
String start = word.substring(0, i);
String end = word.substring(i);
return start + c + end;
}
public static ArrayList<String> getPermutation(String str) {
ArrayList<String> permutations = getPerms(str);
ArrayList<String> res3 = new ArrayList();
String max = new String();
int flag = 0;
int h = permutations.size();
int sum = 0;
while(res3.size() != h){
max=permutations.get(0);
for(int i = 0; i < permutations.size(); i++){
if(max.compareTo(permutations.get(i))<0){
max = permutations.get(i);
flag = i;
}
}
res3.add(new String(max));
permutations.remove(flag);
flag = 0;
sum = 0;
}
return res3;
}2，这是别人写的。
下次再看吧。