165. Compare Version Numbers

Recursion

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public int compareVersion(String version1, String version2) {
    int v1 = 0, v2 = 0;

    int i1 = 0;
    while (i1 < version1.length() && version1.charAt(i1) != '.') {
        v1 = v1 * 10 + (version1.charAt(i1++) - '0');
    }

    int i2 = 0;
    while (i2 < version2.length() && version2.charAt(i2) != '.') {
        v2 = v2 * 10 + (version2.charAt(i2++) - '0');
    }

    int diff = v1 - v2;
    if (diff < 0) {
        return -1;
    } else if (diff > 0) {
        return 1;
    } else {
        if (i1 == version1.length() && i2 == version2.length()) {
            return 0;
        }

        if (i1 == version1.length()) {
            return compareVersion("0", version2.substring(i2 + 1));
        } else if (i2 == version2.length()) {
            return compareVersion(version1.substring(i1 + 1), "0");
        }

        return compareVersion(version1.substring(i1 + 1), version2.substring(i2 + 1));
    }
}

Two Pointers

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class Solution {
    public int compareVersion(String version1, String version2) {
        int i = 0, j = 0;
        while (i < version1.length() || j < version2.length()) {
            int v1 = 0, v2 = 0;
            while (i < version1.length() && version1.charAt(i) != '.') {
                v1 = v1 * 10 + (version1.charAt(i++) - '0');
            }
            i++; // skip dot

            while (j < version2.length() && version2.charAt(j) != '.') {
                v2 = v2 * 10 + (version2.charAt(j++) - '0');
            }
            j++; // skip dot

            if (v1 != v2) {
                return v1 > v2 ? 1 : -1;
            }
        }

        return 0;
    }
}

References

165. Compare Version Numbers