CherubiAI.java
@author: Derek Omuro
@team : No Artificial Flavors
Components
getMove(…)
Iterative-deepening DFS:
explore the tree
examine from leaf to root
0
DFS
1
Bookkeeping:
remember which moves are best
manage array of values
Evaluation function:
evaluate a board configuration
use for leaf nodes
2
3
…
depth-1
depth
h(x)
Interaction between components
Iterative-deepening DFS
public Point getMove(...)
A
depthLimit = 1
while depthLimit != maxDepth
bestMove = search(depthLimit++)
return bestMove
private Point search(...)
B
D
C
E
F
push current state on stack
Example tree; depth limit is 2
while stack isn’t empty
if out of time, return null
node = stack.peek()
while node is not a leaf && node has not been visited
stack.push(possible moves of node)
mark node as visited
node = stack.peek()
stack.pop()
// evaluate and bookkeeping...
G
Bookkeeping
int values[] =
0
1
2
3
...
max depth
-inf
+inf
-inf
+inf
...
±inf
private Point search(...)
node = stack.pop()
B
int value;
if node is a leaf
value = node.evaluate()
1
5
else //node has been visited
value = values[node.depth]
reset values from node.depth to depthLimit
if value is better than values[node.depth-1]
values[node.depth-1] = value
if node.depth == 1
bestMove = node.lastMove
A
max
C
3
min
2
Evaluation Function
Look at every possible win vector
public int evaluate(...)
value = 0
for every possible win vector
value += score(winVector[])
return value
Update points based on pieces in each win vector
O
=5
O
O
private int score(byte winVector[])
if different pieces in winVector
return 0
else
return 5^(# of pieces)*(±1)
= 25
O
O
X
=0
Putting it all together
Point getMove(…)
Iterative-deepening DFS:
Iterative: keep searching one level deeper
DFS: pop from leaves to root
0
Bookkeeping:
You only need a single integer array
Update parent based on child
If updating root, save the last move
DFS
1
2
3
…
depth-1
depth
Evaluation function:
Use to evaluate nodes at depth limit
Look at every possible win vector
…
max depth
h(x)
Interaction between components
Coding Tips
Do not code everything up at once!
1. IDDFS: pop from leaf to root
2. Simple evaluation function
3. Bookkeeping: manage int values[]
4. Improve evaluation function
To do:
Alpha-beta pruning
Much more…