题解 | #合法IP#

#include <stdio.h>
#include <string.h>

int IPv4_verify(char *ip);

int main() {
    char str[18]={0};
    
    scanf("%s", str);
    int flag = IPv4_verify(str);
    
    if(flag)
            printf("YES\n");
    else
        printf("NO\n");
    return 0;
}
int IPv4_verify(char *ip)
{
    int c[4] = {-1};
    int count[4] = {0};

    int n = strlen(ip);

    if(4 == sscanf(ip,"%d.%d.%d.%d", c, c+1, c+2, c+3) )
    {
        for(int i = 0; i<4; i++)
        {
            if(c[i]<=255 && c[i] >=0)
            {
                int temp = c[i];
                if(temp == 0)
                {
                    count[i] = 1;
                }
                else {
                    while(temp > 0){  //求数字长度
                        count[i]++;
                        temp = temp/10;
                    }
                }
            }
            else {
                return 0;
            }
        }

        int sum = 0;  //注意对01.3.8.4为No,通过判断位数与长度是否相等来确定
        for(int i = 0; i<4; i++)
        {
            sum += count[i] + 1;
        }
        if( sum - 1 != n )
        {
            return 0;
        }
       return 1;
    }
    else 
        return 0;

}