public class Solution {
public ArrayList> permute(int[] num) {
ArrayList> result = new ArrayList>();
Arrays.sort(num);
do {
ArrayList list = new ArrayList();
for (int i : num)
list.add(i);
result.add(list);
} while (nextPermutation(num));
return result;
}
private boolean nextPermutation(int[] num) {
int n = num.length;
int descStart = 0;
for (int i = n - 1; i > 0; i--)
if (num[i] > num[i - 1]) {
descStart = i;
break;
}
if (descStart == 0) // there is no bigger number
return false;
for (int i = n - 1; i >= descStart; i--)
if (num[i] > num[descStart - 1]){
swap(num, i, descStart - 1);
break;
}
reverse(num, descStart, n - 1);
return true;
}
private void reverse(int[] n, int s, int e) {
for (; s < e; s++, e--)
swap(n, s, e);
}
private void swap(int[] n, int i, int j) {
int tmp = n[i];
n[i] = n[j];
n[j] = tmp;
}
}