165 Compare Version Numbers

Leetcode

Given two version numbers, version1 and version2, compare them.

Version numbers consist of one or more revisions joined by a dot '.'. Each revision consists of digits and may contain leading zeros. Every revision contains at least one character. Revisions are 0-indexed from left to right, with the leftmost revision being revision 0, the next revision being revision 1, and so on. For example 2.5.33 and 0.1 are valid version numbers.

To compare version numbers, compare their revisions in left-to-right order. Revisions are compared using their integer value ignoring any leading zeros. This means that revisions 1 and 001 are considered equal. If a version number does not specify a revision at an index, then treat the revision as 0. For example, version 1.0 is less than version 1.1 because their revision 0s are the same, but their revision 1s are 0 and 1 respectively, and 0 < 1.

Return the following:

If version1 < version2, return -1.
If version1 > version2, return 1.
Otherwise, return 0.

Example 1:

Input: version1 = "1.01", version2 = "1.001"
Output: 0
Explanation: Ignoring leading zeroes, both "01" and "001" represent the same integer "1".

Example 2:

Input: version1 = "1.0", version2 = "1.0.0" Output: 0 Explanation: version1 does not specify revision 2, which means it is treated as "0". Example 3:

Input: version1 = "0.1", version2 = "1.1"
Output: -1
Explanation: version1's revision 0 is "0", while version2's revision 0 is "1". 0 < 1, so version1 < version2.

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字符串的 split 方法，传递一个正则表达式的字符串，根据匹配结果把字符串分割为字符串数组。如果无法匹配，也会分割为长度为 1 的数组，也就是字符串本身。 Integer 的 valueOf 方法，将字符串转换为整数，转换不了会抛错，转换的时候会自动去掉前面的 0 。

public int compareVersion(String version1, String version2) {
    String[] ss1 = version1.split("\\.");
    String[] ss2 = version2.split("\\.");
    
    for(int i=0;i<ss1.length || i<ss2.length;++i){
        int i1 = i<ss1.length ? Integer.valueOf(ss1[i]):0;
        int i2 = i<ss2.length ? Integer.valueOf(ss2[i]):0;
        int cmp = i1-i2;
        if(cmp==0) continue;
        return cmp>0?1:-1;
    }
    return 0;
}