用TDD来实现华为机试题-求质数因子

题目网址

质数因子-牛客网

算法解读

输入

要求

1. 1个
2. long型整数

算法

质数因子的概念参考
质数因子分解

思路

根据对概念的理解，将算法拆为两块：

1. 根据输入long整数，拿到整数内所有的prime质数列表
2. 求质数因子

实现

基于jdk11，源码见
github
prime.factors package

输入类 test

public class UserInputReaderTest {
    @Test
    void inputIsA_positiveInteger() {
        LineReaderStub stub = new LineReaderStub();
        stub.simulateUserInputs("-1", "abc", "0", "180");
        UserInputReader reader = new UserInputReader(stub);
        assertThat(reader.readANumber(), is(180L));
    }
}

其中stub类用来模拟用户的输入

public class LineReaderStub  implements LineReader {
    public List userInputs = new ArrayList<>();
    private int readOffset = 0;

    @Override
    public String readLine() {
        return userInputs.get(readOffset++);
    }

    public void simulateUserInputs(String... inputs) {
        reset();
        Arrays.stream(inputs).forEach(str->userInputs.add(str));
    }

    private void reset() {
        readOffset = 0;
        userInputs.clear();
    }
}

LineReader接口是被驱动出来的，用来抽象不同种类的介质输入，代码如下

public interface LineReader {
    String readLine();
}

输入类 product code

···
public class UserInputReader {
private final LineReader lineReader;

public UserInputReader(LineReader lineReader) { //将输入的异构化作为参数传入，灵活性非常好
    this.lineReader = lineReader;
}

public long readANumber() {
    long result = -1;
    do {
        String line = lineReader.readLine();
        try {
            result = Long.parseLong(line);
        } catch (NumberFormatException e) {
            System.out.println("please input a number");
        }
    } while (result <= 0);
    return result;
}

}
···

求质数因子 test

public class PrimeFactorTest {
    @Test
    void calculatePrimeListWithinInputNumber() {
        int input = 2;
        List primes = PrimeFactor.getPrimeList(input);
        assertThat(primes.size(), is(1));
        assertThat(primes.get(0), is(2L));

        primes = PrimeFactor.getPrimeList(3L);
        assertThat(primes.size(), is(2));

        primes = PrimeFactor.getPrimeList(4L);
        assertThat(primes.size(), is(2));

        primes = PrimeFactor.getPrimeList(5L);
        assertThat(primes.size(), is(3));

        primes = PrimeFactor.getPrimeList(180L);
        assertThat(primes.size(), is(41));
    }

    @Test
    void calcualtePrimeFactor() {
        assertThat(PrimeFactor.getPrimeFactor(12), is(Arrays.asList(2L, 2L, 3L)));
        assertThat(PrimeFactor.getPrimeFactor(147), is(Arrays.asList(3L, 7L ,7L)));
        assertThat(PrimeFactor.getPrimeFactor(17), is(Arrays.asList(17L)));
        assertThat(PrimeFactor.getPrimeFactor(180), is(Arrays.asList(2L, 2L, 3L, 3L, 5L)));
    }

求质数因子 product code

public class PrimeFactor {
    public static List getPrimeList(long n) {
        List result = new ArrayList<>();
        boolean isPrime;
        for (long i = 2; i <= n; i++) {
            if (i % 2 == 0 && i != 2)
                continue; //偶数和1排除
            isPrime = true;
            for (long j = 2; j <= Math.sqrt(i); j++) {
                if (i % j == 0) {
                    isPrime = false;
                    break;
                }
            }

            if (isPrime) {
                result.add(i);
            }
        }
        return result;
    }

    public static List getPrimeFactor(long n) {
        List result = new ArrayList<>();
        List primes = getPrimeList(n);
        long number = n;
        for (Long prime : primes) {
            while (number % prime == 0) {
                result.add(prime);
                number = number / prime;
            }
            if (primes.contains(number)) {
                result.add(number);
                break;
            }
        }
        return result;
    }
}

ATDD main 端到端测试(用console输入输出)

public class Main {
    public static void main(String[] args) {
        LineReader lineReader = ()->new Scanner(System.in).nextLine();
        UserInputReader userInputReader = new UserInputReader(lineReader);
        long inputNumber = userInputReader.readANumber();
        List result = PrimeFactor.getPrimeFactor(inputNumber);
        result.forEach(System.out::println);
    }

}