---
tags: LeetCode
---

# 1154. Day of the Year
Given a string date representing a Gregorian calendar date formatted as YYYY-MM-DD, return the day number of the year.

Example 1:
Input: date = "2019-01-09"
Output: 9
Explanation: Given date is the 9th day of the year in 2019.

Example 2:
Input: date = "2019-02-10"
Output: 41

Example 3:
Input: date = "2003-03-01"
Output: 60

Example 4:
Input: date = "2004-03-01"
Output: 61

Constraints:
date.length == 10
date[4] == date[7] == '-', and all other date[i]'s are digits
date represents a calendar date between Jan 1st, 1900 and Dec 31, 2019.

輸入範本如下

92 ms	24.1 MB
You are here!
Your runtime beats 40.91 % of csharp submissions.
public class Solution {
    public int DayOfYear(string date) {
    }
}

自我限制 : 禁止使用 DateTime 相關物件

136 ms	24 MB
faster than 6.06% of C# online submissions for Day of the Year.
public int DayOfYear(string date)
{
     DateTime d = DateTime.Parse(date);
     return d.DayOfYear;
}

92 ms	24.1 MB
You are here!
Your runtime beats 40.91 % of csharp submissions.
public int DayOfYear(string date)
{
    var dateTime = DateTime.Parse(date);
    var year = dateTime.Year;
    var result = 0;
    while (year == dateTime.Year)
    {
        result++;
        dateTime = dateTime.AddDays(-1);
    }
    return result;
}

### 直覺想法
先查一下閏年的條件...
1. 年能被 400 整除
2. 年能被 4 整除且不能被 100 整除

- 開一個長度十三的陣列做為表 (索引值 0 處 , 不會用到) , 這樣就可以直接使用月份 , 不需要剪一. 另外表內紀錄的是累加天數 , 而非月份天數 , 因此不需要再將月數相加. 就可以得到該月之前的累加天數.
- 使用 Substring 的效能比 Spilt 好 (此題 , 格式固定)

68 ms	22.8 MB
You are here!
Your runtime beats 95.45 % of csharp submissions.
public int DayOfYear(string date)
{
    var days = new int[] {-1, 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };
    int year = int.Parse(date.Substring(0, 4)), month = int.Parse(date.Substring(5, 2)), day = int.Parse(date.Substring(8, 2));
    int isLeap = month > 2 && ((year % 400 == 0) || (year % 4 == 0 && year % 100 != 0)) ? 1 : 0;
    return days[month] + day + isLeap;
}

### Thank you!

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- [GitHub](https://github.com/s0920832252)
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