题目地址：https://leetcode.com/problems/day-of-the-year/
题目描述
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:
1、 date.length==10；
2、 date[4]==date[7]=='-',andallotherdate[i]'saredigits；
3、 daterepresentsacalendardatebetweenJan1st,1900andDec31,2019.；
题目大意
判断给出的日期是当月的第多少天。
解题方法
计算1月1号之间天数
这个题和1185. Day of the Weekopen in new window类似。这个题中计算出当年是不是闰年，然后计算和1月1号之间的天数就行了，需要累加每个月，特别注意二月份。
C++代码如下：
class Solution {
public:
int dayOfYear(string date) {
int year = stoi(date.substr(0, 4));
int month = stoi(date.substr(5, 2));
int day = stoi(date.substr(8));
return countDays(day, month, year);
}
bool isLeapYear(int year) {
return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
}
int countDays(int day, int month, int year) {
int res = 0;
while (month > 1) {
res += daysOfMonth[isLeapYear(year)][month - 2];
month--;
}
res += day;
return res;
}
int daysOfMonth[2][12] = {
{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
{31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
};
};
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