Added Month calendar finder

Added a dynamic programming algorithm to print out a Month's calendar.

Dynamic-Programming/findMonthCalendar.js

@@ -0,0 +1,105 @@
+/*
+*  This algorithm accepts a month in the format mm/yyyy.
+*  And prints out the month's calendar.
+*  It uses an epoch of 1/1/1900, Monday.
+*/
+
+class Month {
+  constructor () {
+    this.Days = ['M', 'T', 'W', 'Th', 'F', 'S', 'Su']
+    this.BDays = ['M', 'Su', 'S', 'F', 'Th', 'W', 'T']
+    this.epoch = { month: 1, year: 1900 }
+    this.monthDays = [31, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
+    this.monthDaysLeap = [31, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
+  }
+
+  printCal (days, startDay) {
+    console.log('M   T   W   Th  F   S   Su')
+    const dates = []; let i
+    for (i = 1; i <= days; i++) {
+      dates.push(i)
+    }
+    for (i = 0; i < this.Days.indexOf(startDay); i++) {
+      dates.unshift(' ')
+    }
+    while (true) {
+      let row = ''
+      for (i = 0; (i < 7) && (dates.length !== 0); i++) {
+        row += dates.shift()
+        while ((row.length % 4) !== 0) {
+          row += ' '
+        }
+      }
+      console.log(row)
+      if (dates.length === 0) break
+    }
+  }
+
+  parseDate (date) {
+    const dateAr = []; let block = ''; let i
+    for (i = 0; i < date.length; i++) {
+      if (date[i] === '/') {
+        dateAr.push(parseInt(block))
+        block = ''
+        continue
+      }
+      block += date[i]
+    }
+    dateAr.push(parseInt(block))
+    if (dateAr.length !== 2) throw new Error('Improper string encoding')
+    const dateOb = { month: dateAr[0], year: dateAr[1] }
+    return dateOb
+  }
+
+  isLeapYear (year) {
+    if (((year % 400) === 0) || (((year % 100) !== 0) && ((year % 4) === 0))) return true
+    else return false
+  }
+
+  isGreater (startDate, endDate) {
+    if (startDate.year > endDate.year) { return true } else if (startDate.year < endDate.year) { return false } else if (startDate.month > endDate.month) { return true } else if (startDate.month < endDate.month) { return false } else return true
+  }
+
+  getDayDiff (startDate, endDate) {
+    if (this.isGreater(startDate, endDate) === null) {
+      return 0
+    } else if ((this.isGreater(startDate, endDate) === true)) {
+      const midDate = startDate
+      startDate = endDate
+      endDate = midDate
+    }
+    let diff = 0
+    while (startDate.year !== endDate.year) {
+      diff += (this.isLeapYear(startDate.year)) ? 366 : 365
+      startDate.year = startDate.year + 1
+    }
+    while (startDate.month !== endDate.month) {
+      if (startDate.month < endDate.month) {
+        if (this.isLeapYear(startDate.year)) diff += this.monthDaysLeap[startDate.month]
+        else diff += this.monthDays[startDate.month]
+        startDate.month = startDate.month + 1
+      } else {
+        if (this.isLeapYear(startDate.year)) diff -= this.monthDaysLeap[startDate.month - 1]
+        else diff -= this.monthDays[startDate.month - 1]
+        startDate.month = startDate.month - 1
+      }
+    }
+    return diff
+  }
+
+  generateMonthCal (date) {
+    const Month = this.parseDate(date); let day = ''
+    let difference = this.getDayDiff(this.epoch, Month)
+    difference = difference % 7
+    let Month2 = this.parseDate(date)
+    day = (this.isGreater(Month2, this.epoch)) ? this.Days[difference] : this.BDays[difference]
+    Month2 = this.parseDate(date)
+    if (this.isLeapYear(Month2.year)) this.printCal(this.monthDaysLeap[Month2.month], day)
+    else this.printCal(this.monthDays[Month2.month], day)
+  }
+}
+
+
+//testing
+const x = new Month()
+x.generateMonthCal('1/2021')