leetcode - 468. 验证IP地址

#include 
#include 
using namespace std;

string isIPv4(string queryIP){
	int n = queryIP.size();
	int tn = 0;
	int flag = 0; // 标记是否是一个数字的开头 
	int num = 0;  // 记录.的个数 
	int count = 0; // 统计每一位数字的个数 
	for(int i = 0; i < n; i++){
		if(queryIP[i] == '.'){
			if(flag == 0 || tn < 0 || tn > 255){
				return "Neither";
			}
			num++; 
			tn = 0;  flag = 0;  count = 0;
		}else if('0' <= queryIP[i] && queryIP[i] <= '9'){
			if(flag == 0){
				if(i+1 < n && queryIP[i] == '0' && queryIP[i+1] != '.'){
					return "Neither";
				}
				flag = 1;
			}
			count++;
			if(count > 3){
				return "Neither";
			}
			tn = tn * 10 + queryIP[i] - '0';
		}else{
			return "Neither";
		}
	}
	if(flag == 0 || tn < 0 || tn > 255 || num != 3){
		return "Neither";
	}
	return "IPv4";
}

string isIPv6(string queryIP){
	int n = queryIP.size();
	int count = 0; 
	int num = 0;  // 记录:的个数 
	for(int i = 0; i < n; i++){
		if(queryIP[i] == ':'){
			if(count < 1 || count > 4){
				return "Neither";
			}
			num++; 
			count = 0;
		}else if(('0' <= queryIP[i] && queryIP[i] <= '9') 
					|| ('A' <= queryIP[i] && queryIP[i] <= 'F')
						|| ('a' <= queryIP[i] && queryIP[i] <= 'f')){
			count++;				
		}else{
			return "Neither";
		}
	} 
	if(count < 1 || count > 4 || num != 7){
		return "Neither";
	}
	return "IPv6";
}

string validIPAddress(string queryIP) {
   	int n = queryIP.size();
	int flag = 0; // 1是判断IPv4  2是判断IPv6 
	string res;
    for(int i = 0; i < n; i++){
		if(queryIP[i] == '.'){
			flag = 1;
			break;
		}else if(queryIP[i] == ':'){
			flag = 2;
			break;
		}
    }  
	if(flag == 1){           // IPv4判断
		res = isIPv4(queryIP);
	}else if(flag == 2){	// IPv6判断
		res = isIPv6(queryIP);
	}else if(flag == 0){	// 不符合4和6的要求 
		res = "Neither";
	}
	return res;
}

int main(){
	string queryIP, res;
	cin>>queryIP; 
	res = validIPAddress(queryIP);
	cout<