165. Compare Version Numbers

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本文介绍了一种用于比较软件版本号的算法实现。该算法通过解析版本号字符串，并将其拆分为多个部分进行逐位比较，从而确定两个版本之间的大小关系。

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

The idea is simple:

Code:

public class Solution {
    public int compareVersion(String version1, String version2) {
        String[] v1 = ("1.1." + version1).split("\\.");
        String[] v2 = ("1.1." + version2).split("\\.");
        int i = 0;
        
        while(i < v1.length && i < v2.length){
            int i1 = Integer.parseInt(v1[i]);
            int i2 = Integer.parseInt(v2[i]);
            if(i1 > i2){
                return 1;
            } else if(i1 < i2){
                return -1;
            } else{
                i++;
            }
        }
        
        
        while(i < v1.length){
            if(Integer.parseInt(v1[i]) != 0){
                return 1;
            }
            i++;
        }
    
        while(i < v2.length){
            if(Integer.parseInt(v2[i]) != 0){
                return- 1;
            }
            i++;
        }
        
        return 0;
    }
}

This Question is Simple, but still something need to remember:

1. Java Split a String , should path a regex, not a String, if split(".") it will return an empty array.

2. for those questions that v1 and v2 has different length, like this question or add two String, there are 2 solutions.

a. use three while loop like this.

b. use one while loop, and in the while loop make additional judgement, if index exceeds the boundary give it a default value. Like the code below from https://discuss.leetcode.com/topic/6238/accepted-small-java-solution/2

public int compareVersion(String version1, String version2) {
    String[] levels1 = version1.split("\\.");
    String[] levels2 = version2.split("\\.");
    
    int length = Math.max(levels1.length, levels2.length);
    for (int i=0; i<length; i++) {
    	Integer v1 = i < levels1.length ? Integer.parseInt(levels1[i]) : 0;
    	Integer v2 = i < levels2.length ? Integer.parseInt(levels2[i]) : 0;
    	int compare = v1.compareTo(v2);
    	if (compare != 0) {
    		return compare;
    	}
    }
    
    return 0;
}