java递归

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
public class test {
public static void main(String[] args) {
ArrayList<ArrayList<Integer>> list = getArrays(1, 20, 30);
Iterator<ArrayList<Integer>> iter = list.iterator();
while (iter.hasNext())
System.out.println(Arrays.toString(iter.next().toArray()));
}

public static int sum(int min, int max) {
if (min > max)
return 0;
return (min + max) * (max - min + 1) / 2;
}

public static ArrayList<ArrayList<Integer>> getArrays(int min, int max, int sum) {
if (sum(min, max) < sum)
return null;
ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();
for (int i = max; i >= min; i--) {
ArrayList<Integer> array;
if (i > sum)
continue;
else if (i == sum) {
array = new ArrayList<Integer>();
array.add(i);
list.add(array);
}
else {
ArrayList<ArrayList<Integer>> temp = getArrays(min, i - 1, sum - i);
if (temp == null)
continue;
Iterator<ArrayList<Integer>> iter = temp.iterator();
while (iter.hasNext()) {
array = iter.next();
array.add(i);
list.add(array);
}
}
}
return list;
}
}