add: slice adv. ops. exercises

16-slices/exercises/25-add-lines/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"
+	"strings"
+
+	s "github.com/inancgumus/prettyslice"
+)
+
+func main() {
+	//
+	// YOU DON'T NEED TO TOUCH THIS
+	//
+	// This inits some options for the prettyslice package.
+	// You can change the options if you want.
+	//
+	// s.Colors(false)     // if your editor is light colored then enable this
+	s.PrintBacking = true  // prints the backing arrays
+	s.MaxPerLine = 15      // prints max 15 elements per line
+	s.SpaceCharacter = "*" // print this instead of printing a newline (for debugging)
+
+	lyric := strings.Fields(`yesterday all my troubles seemed so far away now it looks as though they are here to stay oh i believe in yesterday`)
+
+	// CREATE A LARGE ENOUGH BUFFER
+	// `+3` because we're going to add 3 newline characters
+	fix := make([]string, len(lyric)+3)
+
+	// CALCULATE THE CUT POINTS
+	//
+	// + The first sentence has 8 words so its cutpoint is 8.
+	//
+	// + The second one has 10 words so its cutpoint is 10.
+	//
+	// + The third one has 5 words so its cutpoint is 5.
+	//
+	//
+	// yesterday all my troubles seemed so far away now it looks as though they are here to stay
+	//                                         |
+	//                                         v
+	//                               cutpoint: 8
+	//
+	// ... now it looks as though they are here to stay oh i believe in yesterday
+	//                                             |
+	//                                             v
+	//                                             10
+	//
+	// ... now it looks as though they are here to stay oh i believe in yesterday
+	//                                                                  |
+	//                                                                  v
+	//                                                                  5
+	cutpoints := []int{8, 10, 5}
+
+	// `n` tracks how much we've moved inside the `lyric` slice
+	// `i` tracks the sentence that we're on
+	for i, n := 0, 0; n < len(lyric); i++ {
+		//
+		// copy to `fix` from the `lyric`
+		//
+		//   destination:
+		//     fix[n+i] because we don't want to delete the previous copy.
+		//     it moves sentence by sentence, using the cutpoints.
+		//
+		//   source:
+		//     lyric[n:n+cutpoints[i]] because we want copy the next sentence
+		//     beginning from the number of the last copied elements to the
+		//     n+next cutpoint (the next sentence).
+		//
+		n += copy(fix[n+i:], lyric[n:n+cutpoints[i]])
+
+		// add a newline after the number of copied elements
+		// notice that the '\n' position slides as we move over
+		// that's why n+i
+		fix[n+i] = "\n"
+
+		// uncomment this to aid debugging (to see how the fix slice changes)
+		// s.Show("fix slice", fix)
+	}
+
+	// print the fix slice
+	for _, w := range fix {
+		fmt.Print(w)
+		if w != "\n" {
+			fmt.Print(" ")
+		}
+	}
+}