Project Euler problem 19

project_euler/p019_CountingSundays.py

@@ -1,30 +1,37 @@
-/* Check cf5-opt.vim defs.
-VIM: let g:lcppflags="-std=c++11 -O2 -pthread"
-VIM: let g:wcppflags="/O2 /EHsc /DWIN32"
-VIM: let g:argv=""
-VIM-: let g:cf5output=0
-*/
-#include <iostream>
-#include <exception>
+#Counting Sundays
+#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)?
+# 
 
-/*
-*/
-
-int main ( void )
-{try{
-
-	return 0;
-}
-catch ( const std::exception& e )
-{
-	std::cerr << std::endl
-			<< "std::exception(\"" << e.what() << "\")." << std::endl;
-	return 2;
-}
-catch ( ... )
-{
-	std::cerr  << std::endl
-			<< "unknown exception." << std::endl;
-	return 1;
-}}
+# let's encode sunday 0 - mon 1 ...
+# 1 Jan 1901
+a = 365 #1900 is not a leap year
+a += 1  #1 jan is monday
+a %= 7  #the day of 1 jan 1901
+c = 0   #count of months for which sundays fell on march.
+m = [ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 ]
+for i in range( 1901, 2001 ):
+    for j in range( 1, 13 ):
+        if a==0:
+            c += 1
+        a += m[j-1]
+        if j==2 and i%4==0:
+            a += 1
+        a %= 7
+print(c)