Compare the version number [double pointer to intercept the string you want]

Preface

determine begin/end, It determines a string , Use double pointers to intercept qualified strings . Of course, double pointers do more than that .

One 、 Compare version number

Two 、 Double pointer

package everyday.doublePoint;

//  Compare version number 
public class CompareVersion {
    
    /* target： Compare version1 and version2, Greater than return 1, Less than return -1, Equal return 0.  The comparison of the two is different from the ordinary string comparison , You need to remove the leading 0. */
    public int compareVersion(String version1, String version2) {
    
        int i1 = 0, i2 = 0;
        int j1 = i1, j2 = i2;
        while (j1 < version1.length() || j2 < version2.length()) {
    
            //  Remove the leading as 0.
            while (i1 < version1.length() && version1.charAt(i1) == 0) ++i1;
            //  Count 
            while (++j1 < version1.length() && version1.charAt(j1) != '.') ;
            //  If there is no version number in the subsequent sequence, it will be regarded as 0
            String s1 = i1 >= version1.length() ? "" : version1.substring(i1, j1);
            int val1 = s1 == "" ? 0 : Integer.parseInt(s1);
            //  to update i1/j1
            i1 = ++j1;//  Walk past ellipsis .
            //  Empathy ,i2/j2 such .
            while (i2 < version2.length() && version2.charAt(i2) == 0) ++i2;
            while (++j2 < version2.length() && version2.charAt(j2) != '.') ;
            String s2 = i2 >= version2.length() ? "" : version2.substring(i2, j2);
            int val2 = s2 == "" ? 0 : Integer.parseInt(s2);
            //  to update i2/j2
            i2 = ++j2;//  Walk past ellipsis .
            //  Start comparing 
            if (val1 > val2) return 1;
            if (val1 < val2) return -1;
        }
        return 0;
    }
}

summary

1） Double pointer .

reference

[1] LeetCode Compare version number