leetcode:468. Validate IP Address

原創

2020-02-20 15:37

Write a function to check whether an input string is a valid IPv4 address or IPv6 address or neither.

IPv4 addresses are canonically represented in dot-decimal notation, which consists of four decimal numbers, each ranging from 0 to 255, separated by dots ("."), e.g.,172.16.254.1;

Besides, leading zeros in the IPv4 is invalid. For example, the address 172.16.254.01 is invalid.

IPv6 addresses are represented as eight groups of four hexadecimal digits, each group representing 16 bits. The groups are separated by colons (":"). For example, the address 2001:0db8:85a3:0000:0000:8a2e:0370:7334 is a valid one. Also, we could omit some leading zeros among four hexadecimal digits and some low-case characters in the address to upper-case ones, so 2001:db8:85a3:0:0:8A2E:0370:7334 is also a valid IPv6 address(Omit leading zeros and using upper cases).

However, we don't replace a consecutive group of zero value with a single empty group using two consecutive colons (::) to pursue simplicity. For example, 2001:0db8:85a3::8A2E:0370:7334 is an invalid IPv6 address.

Besides, extra leading zeros in the IPv6 is also invalid. For example, the address 02001:0db8:85a3:0000:0000:8a2e:0370:7334 is invalid.

Note: You may assume there is no extra space or special characters in the input string.

題意：

判斷字符串是否爲合法的IP地址，如果是合法的IPv4地址則返回"IPv4"，如果是合法的IPv6地址則返回"IPv6"，否則返回"Neither"。

解題思路：

純模擬題，主要考察對字符串的處理能力。大致步驟如下：

1.先判斷是何種類型類型的IP地址，進入相應的判別函數，如果都不是就直接返回Neither。

2.構建split()函數，根據分割符個數N將字符串分割爲N+1份（空字符串也爲一份）。

3.若先找到'.'（IPv4分隔符）符號的：

1）先判斷IP在'.'分割符下分割後的段數，若不爲4則直接返回Neither。

2）判斷分割後每段的字符串長度，若爲空串或串長大於3，不合法。

3）判斷每段字符串是否有前導0，有則不合法。

4）判斷字符串中是否有非數字字符，有則不合法。

5）判斷字符串的大小，若大於255則也不合法。

6）若各段字符串均無問題，返回"IPv4"。

4.若先找到':'（IPv6分隔符）符號的：

1）先判斷IP在':'分割符下分割後的段數，若不爲8則直接返回Neither。

2）判斷分割後每段的字符串長度，若爲空串或串長大於4，不合法。

3）判斷字符串中是否有除[0~9a~fA~F]外的字符，有則不合法。

4）若各段字符串均無問題，返回"IPv6"。

實現代碼：

class Solution {
public:
    void split(const string& src, const string& delim, vector<string>& results){
        string str = src;
        int st = 0, ind;
        string substr;
        ind = str.find_first_of(delim, st);
        while(ind != string::npos){
            substr = str.substr(st, ind - st);
            results.push_back(substr);
            st = ind + 1;
            if(st == string::npos){
                results.push_back("");
                return;
            }
            ind= str.find_first_of(delim, st);
        }
        substr = str.substr(st, str.length() - st);
        results.push_back(substr);
        
    }
    string checkIPv4(const string& IP){
        vector<string>results;
        split(IP, ".", results);
        if(results.size() != 4)return "Neither";
        for(int i = 0; i < 4; i++){
            string str = results[i];
            if(str.length() == 0 || str.length() > 3)return "Neither";
            if(str.length() > 1 && str[0] == '0')return "Neither";
            int ind = 0;
            while(ind < str.length()){
                if(str[ind] < '0' || str[ind] > '9')return "Neither";
                ind++;
            }
            int dec = atoi(str.c_str());
            if(dec > 255 || dec < 0)return "Neither";
        }
        return "IPv4";
    }
    string checkIPv6(const string& IP){
        vector<string>results;
        split(IP, ":", results);
        //cout << results.size() << endl;
        if(results.size() != 8)return "Neither";
        for(int i = 0; i < 8; i++){
            string str = results[i];
            if(str.length() == 0 || str.length() > 4)return "Neither";
            int ind = 0;
            while(ind < str.length()){
                char c = str[ind];
                if(c >= '0' && c <= '9' || c >= 'A' && c <= 'F' || c >= 'a' && c <= 'f'){
                    ind++;
                    continue;
                }
                return "Neither";
            }
        }
        return "IPv6";
    }
    string validIPAddress(string IP) {
        vector<string>results;
        int ind = IP.find_first_of(".", 0);
        if(ind != string::npos)return checkIPv4(IP);
        ind = IP.find_first_of(":", 0);
        if(ind != string::npos)return checkIPv6(IP);
        return "Neither";
        
    }
};