Euler problem 19

You are given the following information, but you may prefer to do some research for yourself.

• 1 Jan 1900 was a Monday.
• Thirty days has September,
  April, June and November.
  All the rest have thirty-one,
  Saving February alone,
  Which has twenty-eight, rain or shine.
  And on leap years, twenty-nine.
• A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.

How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?

Solution improvements:

By starting on a Sunday we can add one week each time. Now we only have to check if the Sunday is the first day of the month. Performance boost 5373 us -> 757 us.

Problem19 =         171 elapsed time:    1 ms. Test Passed.