NYOJ 225题 小明求素数积

应用到的知识点：

1.筛选素数（见素数）；

2.大数乘法（见求高精度幂）；

要注意的是：后六位不能以0开头！

 

01.   

02.#include<stdio.h>

03.#include<string.h>

04.intmain()

05.{

06.    booln[1000] = {0};//标记所有的素数；

07.    inti, j;

08.    for(i = 2; i * i <= 1000; i ++)

09.    {

10.        if(n[i] == 0)

11.        for(j = i + i; j <= 1000; j += i )

12.        {

13.            n[j] = 1;

14.        }

15.    }

16.    intT;

17.    scanf("%d", &T);

18.    while(T --)

19.    {

20.        intN;

21.        scanf("%d", &N);

22.        intinput[2000] = {0}, temp[2000] = {0}, output[2000] = {2};

23.        intnum,   out = 1, k = 0, m = 0;//in，input中元素个数；out，output中元素的个数；

24.        for(i = 3; i <= N; i ++)//模拟手算；

25.        {

26.            intj = 0,in = 0;

27.            if(n[i] == 0)//针对所有素数；

28.            {

29.                num = i;

30.                while(num != 0)

31.                {

32.                    input[j ++] = num % 10;

33.                    num /= 10;

34.                    in ++;

35.                }//将素数一位一位地，倒序地，存到input数组里面；

36.                for(j = 0; j < in; j ++)

37.                {

38.                    intl = j, s[2000] = {0}, c[2000] = {0};

39.                    for(k = 0; k < out; k ++)

40.                    {

41.                        s[l] = (c[l] + input[j] * output[k]) % 10;  

42.                        c[l +1] = (c[l] + input[j] * output[k]) / 10;   

43.                        temp[l] += s[l];    

44.                        l ++;

45.                    }

46.                    if(c[l] != 0)

47.                    {

48.                        temp[l] = c[l];

49.                        l = l + 1;

50.                    }

51.                    m = l;

52.                }

53.                out = m;

54.                inttempc[2000] = {0};

55.                for(m = 0; m < out; m ++)

56.                {

57.                    output[m] = (temp[m] + tempc[m]) % 10;  

58.                    tempc[m +1] = (temp[m] + tempc[m]) / 10;    

59.                }

60.                if(tempc[m] != 0)

61.                {

62.                    output[m] = tempc[m];

63.                    out = out + 1;

64.                }

65.                memset(temp, 0, sizeof(temp));//将temp清零；

66.            }

67.        }

68.        if(out <= 6)//总位数<=6, >6, 倒序输出；输出时，竟然还不能以零开头！！！

69.        {

70.            for(i = out - 1; i >= 0; i --)

71.                printf("%d", output[i]);

72.        }

73.        else

74.        {

75.            for(i = 5; i >= 0; i --)

76.            {

77.                 if(output[i] != 0)

78.                     break;

79.            }

80.            for(j = i; j >= 0; j --)

81.                printf("%d", output[j]);

82.        }

83.        printf("\n");

84.    }

85.    return0;

86.}