C 实战练习题目33 – 质数（素数）判断

 1 #include<stdio.h>
 2 #include<math.h>
 3 #define MAX 1000
 4  
 5  
 6 int prime[MAX];
 7  
 8 int isPrimeNaive(int n)
 9 {
10     if(n <= 1)
11         return 0;
12     for(int i = 2; i < n; i++)
13         if(n % i == 0)
14             return 0;
15     return 1;
16 }
17  
18 int isPrime(int n)
19 {
20     if(n<= 1)
21         return 0;
22     if(n == 2)
23         return 1;
24     if(n%2 == 0)
25         return 0;
26     int limit = (int)sqrt((double)n);
27     for(int i = 3; i <= limit; i=i+2)
28     {
29         if(n % i == 0)
30             return 0;
31     }
32     return 1;
33 }
34  
35 void sieve()
36 {
37     prime[0] = 0;
38     prime[1] = 0;
39     for(int i = 2; i < MAX; i++)
40         prime[i] = 1;
41     int limit = (int)sqrt((double)MAX);
42     for(int i = 2; i <= limit; i++)
43     {
44         if(prime[i])
45             for(int j = i*i; j <= MAX; j+=i)
46                 prime[j] = 0;
47     }
48 }
49  
50 int isPrimeSieve(int n)
51 {
52     if(prime[n])
53         return 1;
54     else
55         return 0;
56 }
57  
58 int main()
59 {
60     sieve();
61     printf("N=%d %d\n", 1, isPrime(1));
62     printf("N=%d %d\n", 2, isPrime(2));
63     printf("N=%d %d\n", 3, isPrime(3));
64     printf("N=%d %d\n", 4, isPrime(4));
65     printf("N=%d %d\n", 7, isPrime(7));
66     printf("N=%d %d\n", 9, isPrime(9));
67     printf("N=%d %d\n", 13, isPrime(13));
68     printf("N=%d %d\n", 17, isPrime(17));
69     printf("N=%d %d\n", 100, isPrime(100));
70     printf("N=%d %d\n", 23, isPrime(23));
71     printf("N=%d %d\n", 1, isPrime(1));
72     return 0;
73 }

N=1 0
N=2 1
N=3 1
N=4 0
N=7 1
N=9 0
N=13 1
N=17 1
N=100 0
N=23 1
N=1 0