add: array led clock exercises

15-arrays-project-clock/exercises/04-ticker/solution/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/inancgumus/screen"
+)
+
+func main() {
+	// by using 'shift' we can create the slide effect for placeholders.
+	for shift := 0; ; shift++ {
+		// we need to clear the screen here.
+		// or the previous character will be left on the screen
+		//
+		// alternative: you can fill the rest of the missing placeholders
+		//              with empty lines
+		screen.Clear()
+		screen.MoveTopLeft()
+
+		now := time.Now()
+		hour, min, sec := now.Hour(), now.Minute(), now.Second()
+
+		clock := [...]placeholder{
+			digits[hour/10], digits[hour%10],
+			colon,
+			digits[min/10], digits[min%10],
+			colon,
+			digits[sec/10], digits[sec%10],
+		}
+
+		for line := range clock[0] {
+			l := len(clock)
+
+			// this sets the beginning and the ending placeholders.
+			// to prevent the indexing error: we use the remainder operator.
+			s, e := shift%l, l
+
+			// to slide placeholders from the right part of the screen.
+			//
+			// here, we assume that as if the clock's length is double of its length.
+			// this makes things easy to manage: that's why: l*2 is there.
+			//
+			// whenever, the current shift factor's double remainder is greater than
+			// the length of the clock - 1, it changes the starting and ending positions.
+			if shift%(l*2) > l-1 {
+				s, e = 0, shift%l+1
+			}
+
+			// print empty lines for the right-to-left slide effect.
+			//
+			// this creates the effect of moving placeholders from right to left.
+			for j := 0; j < l-e; j++ {
+				fmt.Print("     ")
+			}
+
+			// draw the digits starting from 's' to 'e'
+			for i := s; i < e; i++ {
+				next := clock[i][line]
+				if clock[i] == colon && sec%2 == 0 {
+					next = "   "
+				}
+
+				fmt.Print(next, "  ")
+			}
+			fmt.Println()
+		}
+
+		time.Sleep(time.Second)
+	}
+}