LeetCode（165） Compare Version Numbers

题目

Compare two version numbers version1 and version2.
If version1 > version2 return 1, if version1 < version2 return -1, otherwise return 0.

You may assume that the version strings are non-empty and contain only digits and the . character.
The . character does not represent a decimal point and is used to separate number sequences.
For instance, 2.5 is not “two and a half” or “half way to version three”, it is the fifth second-level revision of the second first-level revision.

Here is an example of version numbers ordering:

0.1 < 1.1 < 1.2 < 13.37

分析

方法一：
采用字符串比较；此题中的版本比较，需要将.号前的部分与第二部分分开比较；
方法二：
将版本号的字符串转化为整数；

AC代码

class Solution {
public:
    /*方法一：字符串比较；如果version1 > version2 则返回1 相等返回0 反之返回-1*/
    int compareVersion1(string version1, string version2) {
        if (version1.empty() && version2.empty())
            return 0;
        else if (version2.empty())
            return 1;
        else if (version1.empty())
            return -1;
        else
        {
            //分别得到版本号的第一部分和第二部分
            int pos = 0;
            for (int i = 0; version1[i] != '\0' && version1[i] != '.'; ++i)
            {
                ++pos;
            }//for
            string fir_version1;
            string sec_version1;
            if (pos == version1.length())
            {
                fir_version1 = version1;
                sec_version1 = "";
            }
            else{
                fir_version1 = version1.substr(0, pos);
                sec_version1 = version1.substr(pos + 1, version1.length() - pos - 1);
            }
            //要略过第一部分版本号的开头的0
            pos = 0;
            while (fir_version1[pos] != '\0' && fir_version1[pos] == '0')
            {
                ++pos;
            }//while
            if (fir_version1[pos] == '\0')
                fir_version1 = "0";
            else
                fir_version1 = fir_version1.substr(pos, fir_version1.length() - pos);



            pos = 0;
            for (int i = 0; version2[i] != '\0' && version2[i] != '.'; ++i)
            {
                ++pos;
            }//for
            string fir_version2;
            string sec_version2;
            if (pos == version2.length())
            {
                fir_version2 = version2;
                sec_version2 = "";
            }
            else{
                fir_version2 = version2.substr(0, pos);
                sec_version2 = version2.substr(pos + 1, version2.length() - pos - 1);
            }//else

            pos = 0;
            while (fir_version2[pos] != '\0' && fir_version2[pos] == '0')
            {
                ++pos;
            }//while
            if (fir_version2[pos] == '\0')
                fir_version2 = "0";
            else
                fir_version2 = fir_version2.substr(pos, fir_version2.length() - pos);


            if (strcmp(fir_version1.c_str(), fir_version2.c_str()) != 0)
                return strcmp(fir_version1.c_str(), fir_version2.c_str());
            else
                return strcmp(sec_version1.c_str(), sec_version2.c_str());      
        }
    }

    //方法二：化为整数比较
    int compareVersion(string version1, string version2) {
        int val1, val2;
        int idx1 = 0, idx2 = 0;
        while (idx1 < version1.length() || idx2 < version2.length()) {
            val1 = 0;
            while (idx1 < version1.length()) {
                if (version1[idx1] == '.') {
                    ++idx1;
                    break;
                }
                val1 = val1 * 10 + (version1[idx1] - '0');
                ++idx1;
            }
            val2 = 0;
            while (idx2 < version2.length()) {
                if (version2[idx2] == '.') {
                    ++idx2;
                    break;
                }
                val2 = val2 * 10 + (version2[idx2] - '0');
                ++idx2;
            }
            if (val1 > val2) return 1;
            if (val1 < val2) return -1;
        }
        return 0;
    }
};

GitHub测试程序源码