165. Compare Version Numbers

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.

Example 1:

Input: version1 = "0.1", version2 = "1.1"
Output: -1

Example 2:

Input: version1 = "1.0.1", version2 = "1"
Output: 1

Example 3:

Input: version1 = "7.5.2.4", version2 = "7.5.3"
Output: -1

思路

将版本号以点号.分开，借用强大的字符串流stringstream的功能来实现分段并转为整数，再依次进行比较。

这里用到istringstream的状态函数good，用来检查是否没有发生错误，例如是否可执行I/O操作，详见官方文档。

代码

class Solution {
public:
    int compareVersion(string version1, string version2) {
        istringstream v1(version1 + "."), v2(version2 + ".");
        int d1 = 0, d2 = 0;
        //int d1,d2;
        char dot = '.';
        while (v1.good() || v2.good()) {
            //先赋值一个int，再赋值一个char
            if (v1.good()) v1 >> d1 >> dot;
            if (v2.good()) v2 >> d2 >> dot;
            if (d1 > d2) return 1;
            else if (d1 < d2) return -1;
            //这里如果不重置为0的话，出现1.0.1和1这两个版本号的时候处理会出错
            //第一个循环d1=d2=1, 第二个循环d1=0,d2没有值，仍为1，就出现了错误的结果
            d1 = d2 = 0;
        }
        return 0;
    }
};