【leetcode】165.（Medium）Compare Version Numbers

解题思路：

一个字符串两个指针

最初的做法：

class Solution {
    public int compareVersion(String version1, String version2) {
        if(version1==null||version2==null)	return 0;
        
        int len1=version1.length();
        int len2=version2.length();
        int p11=0,p12=0,p21=0,p22=0;
        int num1,num2;
        String str1,str2;
        while(p12<len1&&p22<len2) {
        	while(p12<len1&&version1.charAt(p12)!='.')
        		p12++;
        	while(p22<len2&&version2.charAt(p22)!='.')
        		p22++;
        	str1=version1.substring(p11,p12);
        	str2=version2.substring(p21,p22);
        	
        	num1=Integer.valueOf(str1);
        	num2=Integer.valueOf(str2);
        	if(num1>num2)	return 1;
        	else if(num1<num2)	return -1;	
        	p12++;p22++;p11=p12;p21=p22;
        }
        while(p12<len1) {
        	while(p12<len1&&version1.charAt(p12)!='.')
        		p12++;
        	str1=version1.substring(p11,p12);
        	num1=Integer.valueOf(str1);
        	if(num1>0)	return 1;
        	p12++;p11=p12;
        }
        while(p22<len2){
        	while(p22<len2&&version2.charAt(p22)!='.')
        		p22++;
        	str2=version2.substring(p21,p22);
        	num2=Integer.valueOf(str2);
        	if(num2>0)	return -1;
        	p22++;p21=p22;
        }
        return 0;
    }
}

运行结果：



讨论区有一种正则表达式的做法：

class Solution {
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;
}
}

运行结果：