Euler/cmd/19/main.go

package main

import (
	"fmt"
	"time"
)

func main(){
	weekday := time.Tuesday
	sundays := 0
	for i := 1901; i<=2000; i+=1 {
		var leap int
		if i%4 == 0 {
			leap = 1
		} else {
			leap = 0
		}

		inYearOffset := 0
		//january
		if weekday == 0 {
			sundays += 1
		}
		inYearOffset += 31
		//feb
		if (int(weekday) + inYearOffset) % 7 == 0 {
			sundays += 1
		}
		inYearOffset += 28 + leap
		//march
		if (int(weekday) + inYearOffset) % 7 == 0 {
			sundays += 1
		}
		inYearOffset += 31
		//april
		if (int(weekday) + inYearOffset) % 7 == 0 {
			sundays += 1
		}
		inYearOffset += 30
		//may
		if (int(weekday) + inYearOffset) % 7 == 0 {
			sundays += 1
		}
		inYearOffset += 31
		//june
		if (int(weekday) + inYearOffset) % 7 == 0 {
			sundays += 1
		}
		inYearOffset += 30
		//july
		if (int(weekday) + inYearOffset) % 7 == 0 {
			sundays += 1
		}
		inYearOffset += 31
		//august
		if (int(weekday) + inYearOffset) % 7 == 0 {
			sundays += 1
		}
		inYearOffset += 31
		//september
		if (int(weekday) + inYearOffset) % 7 == 0 {
			sundays += 1
		}
		inYearOffset += 30
		//october
		if (int(weekday) + inYearOffset) % 7 == 0 {
			sundays += 1
		}
		inYearOffset += 31
		//november
		if (int(weekday) + inYearOffset) % 7 == 0 {
			sundays += 1
		}
		inYearOffset += 30
		//december
		if (int(weekday) + inYearOffset) % 7 == 0 {
			sundays += 1
		}
		fmt.Printf("%d: %d\n", i, inYearOffset + 31)


		var offset int
		if i % 4 == 0 {
			offset = (366) % 7
		} else {
			offset = (365)  % 7
		}
		weekday = time.Weekday((offset + int(weekday)) % 7)
	}

	fmt.Printf("Sundays: %d\n", sundays)
}