Recursion Pepper

Another way to loop Call yourself repeatedly until you say to stop. Example: add up 10 numbers using addUp. -- Input – number to count -- Ouput – total of all those numbers added up Logic: If the number I am counting is 0, just return 0. If the number I am counting is anything else, return the number I have + the total of all the rest (the number I have – 1) Requires: Trust the function will do its job A stopper A way to reach the stopper (decrement or increment) Code the addUp method and call it to addUp(10)

Start by trusting it will work Create a method that assumes it will do the job it says it will: Return the number you have + everything else that needed to be done public static int addUp(int numberToCount) { // something else will have to be put here return numberToCount + addUp(numberToCount-1); }

Then, write the stopping code When should it stop calling itself? What should it do in that last case? public static int addUp(int numberToCount) { if (numberToCount == 1) // stop when you are down to #1 { // last called case work return numberToCount;} else { // normal work return numberToCount + addUp(numberToCount-1); }

addUp Solution public class AddUp { public static void main() { System.out.println(addUp(10)); } public static int addUp(int numberToCount) { if (numberToCount == 1) { return numberToCount;} else { return numberToCount + addUp(numberToCount-1); }

Alternative: For public static int addUp(int numberToCount) { int sum = 0; for (int count =1; count <= numberToCount;count++) { sum = sum + count; } return sum; }

Create a string of stars YOU TRY: starString routine -- Input – number of stars needed -- Ouput – String of that many stars Logic: If the number I am counting is 1, just return 1 star. If the number I am counting is anything else, return one star + all the rest of the stars (the number I have – 1) Requires: Trust the function will do its job A stopper A way to reach the stopper (decrement or increment) Code the starString method and call it to create starString(10)

String of Stars public static String starString (int numberStars) { if (numberStars == 0) { return(""); } else { return "*" + starString(numberStars-1); }

Work with shapes Divide a rectangle up 4 levels deep –First print 1 big square –Then divide that one square –Test fully –Then create another method to printInsideSquares with input: level, paintbrush, starting x,y and size. Stop at level 1 – just print the square with no division At every other level, print a big square and printInsideSquares for the smaller squares

Work with Shapes First hint: Here is how to draw 1 level of 4 squares inside 1 square: public static void printOneInsideSquares(int level, Graphics g, int x, int y, int size) { g.drawRect(x,y,size,size); g.drawRect( x,y,size/2,size/2); // top left g.drawRect( x+(size/2), y,size/2,size/2); // top right g.drawRect( x,y+size/2,size/2,size/2); // bottom left g.drawRect( x+size/2,y+size/2,size/2,size/2); // bottom right } Now – add the level logic: stopper: If level == 1, just draw the main rectangle do a job and call itself to do the rest: If level higher, draw main rectangle and printInsideSquares of the small squares at the next level.