题解 | #比较版本号#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 比较版本号
     * @param version1 string字符串
     * @param version2 string字符串
     * @return int整型
     */
    public int compare (String version1, String version2) {
        // write code here
        if (version1 == null && version2 == null) {
            return 0;
        }
        if (version1 == null) {
            return -1;
        }
        if (version2 == null) {
            return 1;
        }
        String[] parts1 = version1.split("\\.");
        String[] parts2 = version2.split("\\.");
        List<String> partList1 = new ArrayList<>(Arrays.asList(parts1));
        List<String> partList2 = new ArrayList<>(Arrays.asList(parts2));
        int len1 = partList1.size();
        int len2 = partList2.size();
        int maxLen = Math.max(len1, len2);
        for (int i = 0; i < maxLen; i++) {
            String str1 = i < len1 ? partList1.get(i) : "";
            String str2 = i < len2 ? partList2.get(i) : "";
            int res = helper(str1, str2);
            if (res != 0) {
                return res;
            }
        }
        return 0;
    }

    private int helper(String part1, String part2) {
        part1 = trimPrefixZero(part1);
        part2 = trimPrefixZero(part2);
        if (part1.equals(part2)) {
            return 0;
        }
        long num1 = part1.equals("") ? 0 : Long.parseLong(part1);
        long num2 = part2.equals("") ? 0 : Long.parseLong(part2);
        return num1 > num2 ? 1 : -1;
    }

    private String trimPrefixZero(String str) {
        char[] arr = str.toCharArray();
        if (arr.length < 1) {
            return str;
        }
        int i = 0;
        while (i < arr.length && arr[i] == '0') {
            i++;
        }
        return i == arr.length ? "" : str.substring(i);
    }

}