領(lǐng)扣題目 一年中的第幾天
兩種解法，第一種邏輯算法寫，效率高，第二種使用jdk的API,效率低，推薦第一種，親測可用：

1.邏輯算法寫

   public class Demo11 {
    public static void main(String[] args) {
        String date1 = "2019-01-09";
        String date2 = "2019-02-10";
        String date3 = "2003-03-01";
        String date4 = "2004-03-01";
        String date5 = "1900-03-25";
        System.out.println(dayOfYear(date1));
        System.out.println(dayOfYear(date2));
        System.out.println(dayOfYear(date3));
        System.out.println(dayOfYear(date4));
        System.out.println(dayOfYear(date5));
    }
    /*平年二月28天*/
    private static final int DAYS_28 = 28;
    /*閏年二月29天*/
    private static final int DAYS_29 = 29;
    /*除了31天的月份其他均為30天*/
    private static final int DAYS_30 = 30;
    /*1、3、5、7、8、10、12月份31天*/
    private static final int DAYS_31 = 31;

    public static int dayOfYear(String date) {
        String[] split = date.split("-");
        int totalDays = 0;
        int year = Integer.valueOf(split[0]);
        int month = Integer.valueOf(split[1]);
        int day = Integer.valueOf(split[2]);
        switch (month) {
            // 12 月份加的是11月份的天數(shù)，依次類推
            case 12:
                totalDays += DAYS_30;
            case 11:
                totalDays += DAYS_31;
            case 10:
                totalDays += DAYS_30;
            case 9:
                totalDays += DAYS_31;
            case 8:
                totalDays += DAYS_31;
            case 7:
                totalDays += DAYS_30;
            case 6:
                totalDays += DAYS_31;
            case 5:
                totalDays += DAYS_30;
            case 4:
                totalDays += DAYS_31;
            case 3:
                // 判斷是否是閏年
                if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0)) {
                    totalDays += DAYS_29;
                } else {
                    totalDays += DAYS_28;
                }
            case 2:
                totalDays += DAYS_31;
            case 1: // 如果是1月份就加上輸入的天數(shù)
                totalDays += day;
        }
        return totalDays;
    }
}

2.使用JDK的API

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;

public class Demo11 {
    public static void main(String[] args) {
        String date1 = "2019-01-09";
        String date2 = "2019-02-10";
        String date3 = "2003-03-01";
        String date4 = "2004-03-01";
        String date5 = "1900-03-25";

        System.out.println(dayOfYear1(date1));
        System.out.println(dayOfYear1(date2));
        System.out.println(dayOfYear1(date3));
        System.out.println(dayOfYear1(date4));
        System.out.println(dayOfYear1(date5));
    }

    public static int dayOfYear1(String date) {
        try {
            Calendar ca = Calendar.getInstance();
            ca.setTime(new SimpleDateFormat("yyyy-MM-dd").parse(date));
            return ca.get(Calendar.DAY_OF_YEAR);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return 0;
    }
}

3.兩種方式的效率

領(lǐng)扣效率比較

比較起來我推薦第一種，當(dāng)然也有借鑒網(wǎng)上大佬的代碼，在此感謝。