Sync

Task/Five-weekends/JavaScript/five-weekends-1.js

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+function startsOnFriday(month, year)
+{
+ // 0 is Sunday, 1 is Monday, ... 5 is Friday, 6 is Saturday
+ return new Date(year, month, 1).getDay() === 5;
+}
+function has31Days(month, year)
+{
+ return new Date(year, month, 31).getDate() === 31;
+}
+function checkMonths(year)
+{
+ var month, count = 0;
+ for (month = 0; month < 12; month += 1)
+ {
+  if (startsOnFriday(month, year) && has31Days(month, year))
+  {
+   count += 1;
+   document.write(year + ' ' + month + '<br>');
+  }
+ }
+ return count;
+}
+function fiveWeekends()
+{
+ var
+  startYear = 1900,
+  endYear = 2100,
+  year,
+  monthTotal = 0,
+  yearsWithoutFiveWeekends = [],
+  total = 0;
+ for (year = startYear; year <= endYear; year += 1)
+ {
+  monthTotal = checkMonths(year);
+  total += monthTotal;
+  // extra credit
+  if (monthTotal === 0)
+   yearsWithoutFiveWeekends.push(year);
+ }
+ document.write('Total number of months: ' + total + '<br>');
+ document.write('<br>');
+ document.write(yearsWithoutFiveWeekends + '<br>');
+ document.write('Years with no five-weekend months: ' + yearsWithoutFiveWeekends.length + '<br>');
+}
+fiveWeekends();

Task/Five-weekends/JavaScript/five-weekends-2.js

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+var Months = [
+  'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
+  'Jul', 'Aug', 'Sept', 'Oct', 'Nov', 'Dec'
+];
+
+var leap = 0,
+  // Relative offsets between first day of each month
+  offset = [3,0,3,2,3,2,3,3,2,3,2,3],
+
+  // Months that contain 31 days
+  longMonths = [1,3,5,7,8,10,12],
+
+  startYear = 1900,
+  year = startYear,
+  endYear = 2100,
+
+  // Jan 1, 1900 starts on a Monday
+  day = 1,
+
+  totalPerYear = 0,
+  total = 0,
+  without = 0;
+
+for (; year < endYear + 1; year++) {
+  leap = totalPerYear = 0;
+
+  if (year % 4 === 0) {
+    if (year % 100 === 0) {
+      if (year % 400 === 0) {
+        leap = 1;
+      }
+    } else {
+      leap = 1;
+    }
+  }
+
+  for (var i = 0; i < offset.length; i++) {
+    for (var j = 0; day === 5 && j < longMonths.length; j++) {
+      if (i + 1 === longMonths[j]) {
+        console.log(year + '-' + Months[i]);
+        totalPerYear++;
+        total++;
+        break;
+      }
+    }
+
+    // February -- if leap year, then +1 day
+    if (i == 1) {
+      day = (day + leap) % 7;
+    } else {
+      day = (day + offset[i]) % 7;
+    }
+  }
+
+  if (totalPerYear === 0) {
+    without++;
+  }
+}
+
+console.log('Number of months that have five full weekends from 1900 to 2100: ' + total);
+console.log('Number of years without any five full weekend months: ' + without);