日期格式转换代码部分测试用例失败问题排查

我正在解决将“Day Month Year”格式的日期字符串转换为YYYY-MM-DD格式的问题，要求如下：

• 输入日期中，Day是带后缀的数字（如1st、2nd），Month是三位缩写（如Jan、Feb），Year范围在[1900,2100]
• 输出需为4位年份、2位月份、2位日期的YYYY-MM-DD格式

部分测试用例能正常通过，比如输入“20th Oct 2052”时输出正确的2052-10-20，但输入“26th May 1960”时输出1960-5-26，正确结果应为1960-05-26，以下是我的代码：

class Solution(object):
    def reformatDate(self, date):
        list_date = date.split()
        YYYY = ""
        MM = ""
        DD = ""

        DD_dict = {
            "1st": "1", "2nd": "2", "3rd": "3", "4th": "4",
            "5th": "5", "6th": "6", "7th": "7", "8th": "8", "9th": "9", "10th": "10",
            "11th": "11", "12th": "12", "13th": "13", "14th": "14", "15th": "15", "16th": "16",
            "17th": "17", "18th": "18", "19th": "19", "20th": "20", "21st": "21", "22nd": "22",
            "23rd": "23", "24th": "24",
            "25th": "25", "26th": "26", "27th": "27", "28th": "28", "29th": "29", "30th": "30", "31st": "31"
        }

        MM_dict = {
            "Jan": "1", "Feb": "2", "Mar": "3", "Apr": "4",
            "May": "5", "Jun": "6", "Jul": "7", "Aug": "8", "Sep": "9", "Oct": "10",
            "Nov": "11", "Dec": "12"
        }

        for char in list_date:
            if char in DD_dict:
                if int(DD_dict[char]) < 10:
                    DD += '0' + DD_dict[char]
                else:
                    DD += DD_dict[char]
            elif char in MM_dict:
                if int(MM_dict[char]) < 10:
                    MM += '0' + MM_dict[char]
                else:
                    MM += MM_dict[char]
            else:
                YYYY += char

        return "".join(f'{int(YYYY)}-{int(MM)}-{int(DD)}')


if __name__ == '__main__':
    date = "20th Oct 2052"
    d2 = "26th May 1960"

    print(Solution().reformatDate(date))
    print(Solution().reformatDate(d2))

错误原因分析 #

问题出在最后的返回语句：

return "".join(f'{int(YYYY)}-{int(MM)}-{int(DD)}')

• 你已经在前面的逻辑中为月份和日期补了前导零（比如May对应的MM会被处理成"05"），但这里将MM和DD转换为整数时，前导零会被自动移除，导致输出变成5而非05
• 另外，"".join()在这里完全多余，因为f-string本身已经是完整的字符串

修复方案 #

直接返回拼接好的字符串，不需要转换为整数：

return f'{YYYY}-{MM}-{DD}'

可选优化方案 #

可以提前在字典中存储带前导零的字符串，省去判断补零的逻辑，让代码更简洁：

DD_dict = {
    "1st": "01", "2nd": "02", "3rd": "03", "4th": "04",
    "5th": "05", "6th": "06", "7th": "07", "8th": "08", "9th": "09", "10th": "10",
    "11th": "11", "12th": "12", "13th": "13", "14th": "14", "15th": "15", "16th": "16",
    "17th": "17", "18th": "18", "19th": "19", "20th": "20", "21st": "21", "22nd": "22",
    "23rd": "23", "24th": "24",
    "25th": "25", "26th": "26", "27th": "27", "28th": "28", "29th": "29", "30th": "30", "31st": "31"
}

MM_dict = {
    "Jan": "01", "Feb": "02", "Mar": "03", "Apr": "04",
    "May": "05", "Jun": "06", "Jul": "07", "Aug": "08", "Sep": "09", "Oct": "10",
    "Nov": "11", "Dec": "12"
}

之后处理逻辑可以简化为：

for char in list_date:
    if char in DD_dict:
        DD = DD_dict[char]
    elif char in MM_dict:
        MM = MM_dict[char]
    else:
        YYYY = char

内容的提问来源于stack exchange，提问作者klaus19