实践递归

描述：1,2,3......n 从n中取出r个数。
例如：n=5，r=3
1-2-3，1-2-4，1-2-5，1-3-4，1-3-5，1-4-5
2-3-4，2-3-5，2-4-5
3-4-5

下面是我的解决方法，还有其他的方法么？

java 代码

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.Stack;

public class Combination {
    private List result;
    private int r = 4;
    private int n = 7;

    public Combination() {
        result = new ArrayList();
        Stack permutation = new Stack();
        for (int i = 1; i < r + 1; i++) {
            permutation.push(i);
        }
        result.add(permutation);
    }

    public static void main(String[] args) {
        Combination com = new Combination();
        com.compose(com.result.size());
        com.removeExisted();
        com.sortList();
        com.print();
    }

    private void sortList() {
        List sorted = new ArrayList();
        for (Iterator iter = result.iterator(); iter.hasNext();) {
            Stack element = (Stack) iter.next();
            StringBuffer sb = new StringBuffer();
            for (Iterator iterator = element.iterator(); iterator.hasNext();) {
                int i = (Integer) iterator.next();
                sb.append(i + "-");
            }
            sb.deleteCharAt(sb.length()-1);
            sorted.add(sb.toString());
        }
        Collections.sort(sorted);
        result=sorted;
    }

    private void removeExisted() {
        Set set = new HashSet();
        for (Iterator iter = result.iterator(); iter.hasNext();) {
            set.add(iter.next());
        }
        result.clear();
        result.addAll(set);
    }

    private void print() {
        System.out.println("result:");
        for (Iterator iter = result.iterator(); iter.hasNext();) {
            String element = (String) iter.next();
            System.out.println(element);
        }
    }

    private void compose(int size) {
        for (int i = 0; i < size; i++) {
            Stack element = (Stack) result.get(i);
            int max = (Integer) element.peek();
            if (max == n) {
                return;
            } else {
                Stack copyedS = copyStack(element);
                ++max;
                createNewComS(copyedS, max);
            }
        }
        compose(result.size());
    }

    private void createNewComS(Stack original, int max) {
        for (int i = 0; i < r; i++) {
            Stack copyedS = copyStack(original);
            copyedS.remove(i);
            copyedS.push(max);
            result.add(copyedS);
        }
    }

    private Stack copyStack(Stack element) {
        Stack copyed = new Stack();
        for (int i = 0; i < element.size(); i++) {
            int num = (Integer) element.get(i);
            copyed.push(num);
        }
        return copyed;
    }
}