题解 | #识别有效的IP地址和掩码并进行分类统计#

#include <stdio.h>
#include <string.h>
#define VALIDIP(a, b, c, d) (a >= 0 && a < 256 && \
                             b >= 0 && b < 256 &&\
                             c >= 0 && c < 256 &&\
                             d >= 0 && d < 256 )

int is_mask_valid(unsigned int a, unsigned int b, unsigned int c, unsigned int d){
    unsigned int m = -1;
    unsigned int mask;
    
    mask = (a << 24) | (b << 16) | (c << 8) | d;
    if (mask == m || mask == 0)
        return 0;
    for (; (mask & 1) == 0; mask >>= 1, m >>= 1)
        ;
    return mask == m;
}
int main(){
    int a, b, c, d, e, invalid, private;
    int s1, s2, s3, s4, m1, m2, m3, m4;
    char s[40];
    char ip[20], mask[20];
    
    a = 0, b = 0, c = 0, d = 0, e = 0, invalid = 0, private = 0;
    while (scanf("%s", s) == 1){
		sscanf(s, "%[^~]", ip);
		sscanf(s+strlen(ip)+1, "%s", mask);
		 // process ip
		if ((sscanf(ip, "%d.%d.%d.%d", &s1, &s2, &s3, &s4) == 4) && VALIDIP(s1, s2, s3, s4)){
			if (s1 == 0 || s1 == 127)
				continue;	
			// process mask
			if ((sscanf(mask, "%d.%d.%d.%d", &m1, &m2, &m3, &m4) == 4)
			   && is_mask_valid(m1, m2, m3, m4)){
				if (s1 < 127){
					a++;
					if (s1 == 10) private++;
				}
				else if (s1 < 191){
					b++;
					if (s1 == 172 && s2 >= 16 && s2 <= 31) private++;
				} 
				else if (s1 < 223) {
					c++;
					if (s1 == 192 && s2 == 168) private++;
				}
				else if (s1 < 239) d++;
				else               e++;
			}else{
				invalid++;   
			}  				
		}else{
			invalid++;
			continue;
		}
    }
    printf("%d %d %d %d %d %d %d", a, b, c, d, e, invalid, private);
    return 0;
}