大学のプログラミング課題ができません。

maria_salon1984さん

なんか…久しぶりに…
難しかった orz

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.TreeMap;

public class Sample {
public static void main(String[] args) {
Sample sample = new Sample();
sample.start();
}

private void start() {
try {
BufferedReader br = new BufferedReader(new InputStreamReader(
System.in));
System.out.println("所持金を入力してください");
int pocket = Integer.parseInt(br.readLine());
TreeMap<Integer, Integer> pocketMap = initArray(pocket);
System.out.println("支払い金額を入力してください");
int amount = Integer.parseInt(br.readLine());
System.out.println("計算します");
TreeMap<Integer, Integer> pay = calc(amount, pocket, pocketMap);
System.out.println("支払うのは");
int sum = 0;
for (Integer key : pay.keySet()) {
if (pay.get(key) != 0)
System.out.println(key + "円を" + pay.get(key) + "枚");
sum += key * pay.get(key);
}
System.out.println("支払い金額は" + sum + "です。");
System.out.println("おつりは" + (sum - amount) + "円です");
} catch (NumberFormatException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}

public TreeMap<Integer, Integer> calc(int amount, int pocket,
TreeMap<Integer, Integer> pocketMap) {
TreeMap<Integer, Integer> pay = new TreeMap<Integer, Integer>();
int[] coinArray = { 1000, 500, 100, 50, 10, 5, 1 };
amount = pocket - amount;
if (amount < 0) {
throw new IllegalArgumentException("Not enough");
}
for (int coin = 0; coin < coinArray.length; coin++) {
int m = (pocketMap.get(coinArray[coin]) != null) ? pocketMap
.get(coinArray[coin]) : 0;
if (m - amount / coinArray[coin] >= 0) {
pay.put(coinArray[coin], m - amount / coinArray[coin]);
}
amount %= coinArray[coin];
}
return pay;
}

private TreeMap<Integer, Integer> initArray(int pocket) {
TreeMap<Integer, Integer> purse = new TreeMap<Integer, Integer>();
int array[] = { 1000, 500, 100, 50, 10, 5, 1 };
for (int i = 0; i < array.length; i++) {
int num = pocket / array[i];
System.out.println(array[i] + "円は" + num + "枚です");
purse.put(array[i], num);
pocket -= num * array[i];
}
return purse;
}
}