public class Equals1 {
    //    面值
    int[] values= {100,50,30,20};
    int[] zhangshu = {0,0,0,0};//张数
//  库存
    HashMap<Integer, Integer> invoiceMap=new HashMap<Integer, Integer>();
    int total = 150;
    public Equals1(){
        invoiceMap.put(30,3);
        invoiceMap.put(50,3);
        invoiceMap.put(20,5);
        invoiceMap.put(100,2);
    }
    public int action(int index,int tail){
        if(index>values.length - 1){
            return -1;
        }
        zhangshu[index] = Math.min(tail/values[index],invoiceMap.get(values[index]));
        tail -= zhangshu[index]*values[index];
        if(tail==0){
            return 0;
        }
        else{
            for(int i= 0;i <=zhangshu[index];zhangshu[index]--){
                 if(action(index+1,tail)==0){
                     return 0;
                 }
                 tail += values[index];
            }
        }
        return tail;
    }
    public static void main(String[] args) {
        Equals1 a = new Equals1();
        int total = 500;
        a.action(0,total);
        if(a.action(0,total)==0){
            for(Integer it:a.zhangshu){
                System.out.print(it+" ");    
            }
        }
        else{
            System.out.print("不能分配该数字。");    
        }
    }
}

------解决方案--------------------
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;

import org.junit.Test;

public class FP {
	HashMap<Integer, Long> invoiceMap = new HashMap<Integer, Long>();// 存放发票面额和库存

	ArrayList<Integer> list = new ArrayList<Integer>();

	public FP() {
		invoiceMap.put(30, 10L);
		invoiceMap.put(50, 3L);
		invoiceMap.put(20, 5L);
		invoiceMap.put(100, 10L);

		Set<Integer> set = invoiceMap.keySet();
		Iterator<Integer> it = set.iterator();
		while (it.hasNext()) {
			list.add(it.next());
		}
		Collections.sort(list);
		Collections.reverse(list);
		// int total = 130;
	}

	public HashMap<Integer, Long> invoiceMethod(
			HashMap<Integer, Long> invoiceMap, int total) {

		for (int i = 0; i < list.size(); i++) {

			if (total >= (Integer) list.get(i)) {
				int count = total / list.get(i);

				// invoiceMap 的数值发生变化
				invoiceMap
						.put(list.get(i), invoiceMap.get(list.get(i)) - count);
				// total 减少数据
				total -= count * list.get(i);
			}
		}
		return invoiceMap;
	}

	private void pt(Object integer) {
		System.out.println(integer);
	}

	@Test
	public void t() {
		FP f = new FP();
		invoiceMethod(invoiceMap, 150);
		pt(invoiceMap);
	}
}