1. More Recursion

2. Binary Strings "" 3 steps to go "0" "1" 2 steps to go "00" "01" "10"
"11"
1 step to go
"000"
"001"
"010"
"011"
"100"
"101"
"110"
"111"
done

3. Binary Strings

4. Towers Of Hanoi 3 Pegs & Stack of disks Get from one peg to another
Can only move one disk at a time
Big disks can not be on top of small disks

5. Decomposition To move 3 disks from A to C
Move top 2 to B Move last to C Move 2 from B to C

6. Towers Of Hanoi
3 disks = 7 moves
N disks = 2n – 1 moves

7. N-Queens
Eight Queens
Each must be on own row/col/diagonal

8. Representation
Single array : what col is queen in?

9. Code
Do not need to copy – moving queen overwrites old move

10. Flood Fill Flood Fill Color starting square Try to color square above
Try to color square below
Try to color square to left
Try to color square to right

11. Shared Data Flood fill works on one copy of data
Array passed as memory addresses
Every recursive call uses same array

12. Path Finding Find a path… If goal, done = return 0
If bad square return 
Else
Mark square
Ask left how far
Ask right how far
Ask up how far
Ask down how far
Return 1 + shortest of neighbors

13. Path Finding

14. Path Finding Want to explore different paths Each path needs own array
Need to copy current maze before marking move