题解 | #验证IP地址#

#include <stdbool.h>
#include <string.h>
int counter(char* str, char s){
    int count=0;
    for (int i=0; i<strlen(str); i++) {
        if (str[i]==s) {
            count++;
        }
    }
    return count;
}

bool isDigit(const char ch){
    if (ch>='0'&&ch<='9') return true;
    return false;
}
bool isDigit16(const char ch){
    if (ch>='0'&&ch<='9') return true;
    if (ch>='A'&&ch<='F') return true;
    if (ch>='a'&&ch<='f') return true;
    return false;
}

bool isValidIPv4(char* IP){
    int len=strlen(IP);
    if(counter(IP,'.')!=3)return false;//保证只有4个区间
    if (IP[len]=='.') return false;
    int left=0,right=0;
    while (right<len) {
        right=left;
        while (right<len&&IP[right]!='.') {
            if (!isDigit(IP[right])) return false;//保证区间内都是数字
            right++;
        }
        if (left==right||right>left+3) return false;//保证区间长度
        int cur=0;
        for (int i=left; i<right; i++) cur=cur*10+IP[i]-'0';
        if (cur>255||(cur>=0&&IP[left]=='0')) return false;//保证区间内的数符合规定
        left=right+1;//开始找下一区间
    }
    return true;
}

bool isValidIPv6(char* IP){
    int len=strlen(IP);
    if(counter(IP,':')!=7)return false;
    if (IP[len]==':') return false;
    int left=0,right=0;
    while (right<len) {
        right=left;
        while (right<len&&IP[right]!=':') {
            if (!isDigit16(IP[right])) return false;
            right++;
        }
        if (left==right||right>left+4) return false;
        left=right+1;  
    }
    return true;
}

char* solve(char* IP ) {
    // write code here
    if (isValidIPv4(IP)) return "IPv4";
    else if (isValidIPv6(IP)) return "IPv6";
    return "Neither";
}