---
title: 'LeetCode 1154. Day of the Yearr'
disqus: hackmd
---

# LeetCode 1154. Day of the Year

## Description

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

## Example

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

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

## 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^th^, 2019.

## Answer

此題是計算該年1/1至給定的日期共有幾天，首先將年月日都先讀取出來，然後用一個for從1月開始算，算到給定的月份前，其中在計算日期的時候還要判斷現在是不是閏年，若是的話2月就有29天，在月份日期的規律中，8月以下的奇數月有31天，除2月以外的偶數月有30天，從8月開始就是反過來，如此依序疊加日期，最後再加上題目給定的天數即為答案。

判斷閏年就是用因數方法，若是4的倍數但不為100的倍數且又是400的倍數，則該年為閏年。

int str2int(char *date);
int IsLeapYear(int year);

int dayOfYear(char * date){
    int YY = 0, MM = 0, DD = 0, ans = 0;
    DD = str2int(date+8);
    MM = str2int(date+5);
    YY = str2int(date);
    for(int i = 1; i < MM; i++){
        if(i < 8){
            if(i==2){
                if(IsLeapYear(YY)){ans += 29;}
                else{ans += 28;}
            }
            else if(i&1){ans += 31;}
            else{ans += 30;}
        }
        else{
            if(i&1){ans += 30;}
            else{ans += 31;}
        }
    }
    return ans + DD;
}

int str2int(char *date){
    int ans = 0;
    while(*date >= '0' && *date <= '9'){
        ans = ans*10 + (*date - '0');
        date++;
    }
    return ans;
}

int IsLeapYear(int year){
    int ans = 0;
    if((year%4==0 && year%100 != 0) || (year%400 == 0)){
        ans = 1;
    }
    return ans;
}

## Link
https://leetcode.com/problems/day-of-the-year/
###### tags: `Leetcode`