From 9f270071fb17de7dc822a38c5fd020b6edb8e1cc Mon Sep 17 00:00:00 2001
From: Sailesh <saileshsimhadri@gmail.com>
Date: Wed, 19 Apr 2017 16:24:49 -0400
Subject: [PATCH] Implement variable depth minimax

---
 src/CheckersAI.java         | 35 ++++++++++++++++++-----------------
 src/CheckersGameState3.java |  2 +-
 src/RmCheckersClient.java   |  2 +-
 3 files changed, 20 insertions(+), 19 deletions(-)

diff --git a/src/CheckersAI.java b/src/CheckersAI.java
index f761434..36a5b07 100644
--- a/src/CheckersAI.java
+++ b/src/CheckersAI.java
@@ -9,21 +9,24 @@ public class CheckersAI{
         this.player = player;
     }
 
-    private boolean stop(CheckersGameState state, boolean jumped, int depth){
+    private boolean stop(CheckersGameState state, boolean jumped, int depth, int min_ply){
         CheckersGameState3 s = (CheckersGameState3) state;
-        if(!s.canJump() && !jumped && !s.canExchange() && depth == 3){
+        if(depth < min_ply){
+            return false;
+        }
+        else if(depth == min_ply && !s.canJump() && !jumped && !s.canExchange()){
            return true;
         }
-        else if(!s.canJump() && !s.canExchange() && depth == 4){
+        else if(depth == min_ply +1 && !s.canJump() && !s.canExchange() && depth == 4){
             return true;
         }
-        else if(depth < 11 && !s.canJump()){
+        else if(depth > min_ply +1 && depth < min_ply + 10  && !s.canJump()){
             return true;
         }
-        else if(depth < 20 && s.twoKings()){
+        else if(depth > min_ply +10 && depth < min_ply + 20 && s.twoKings()){
             return true;
         }
-        else if(depth >=  20){
+        else if(depth >=  min_ply + 20){
             return true;
         }
         else{
@@ -31,7 +34,7 @@ public class CheckersAI{
         }
     }
 
-    public Move minimax(CheckersGameState s){
+    public Move minimax(CheckersGameState s, int min_ply){
         int depth = 0;
         if(s.isTerminal()){
             return null;
@@ -43,7 +46,7 @@ public class CheckersAI{
         Move max = null;
         // System.out.println(s.actions().size());
         for(Move a: s.actions()){
-            check = minValue(s.result(a), alpha, beta, depth + 1, a.isJump());
+            check = minValue(s.result(a), alpha, beta, depth + 1, a.isJump(), min_ply);
             if(check > v){
                 v = check;
                 max = a;
@@ -56,15 +59,14 @@ public class CheckersAI{
         return max;
     }
 
-   private double maxValue(CheckersGameState s, double alpha, double beta, int depth, boolean jumped){
-
-        if(s.isTerminal() || stop(s, jumped, depth)){
-         return eval.evaluate(s, this.player); // if terminal, piece ratio should be infinite
+   private double maxValue(CheckersGameState s, double alpha, double beta, int depth, boolean jumped, int min_ply){
+        if(s.isTerminal() || stop(s, jumped, depth, min_ply)){
+             return eval.evaluate(s, this.player); // if terminal, piece ratio should be infinite
         }
         double v = Double.NEGATIVE_INFINITY;
         double check;
         for(Move a: s.actions()){
-            check = minValue(s.result(a), alpha, beta, depth + 1, a.isJump());
+            check = minValue(s.result(a), alpha, beta, depth + 1, a.isJump(), min_ply);
             if(check > v){
                 v = check;
             }
@@ -76,15 +78,14 @@ public class CheckersAI{
         return v;
     }
 
-   private double minValue(CheckersGameState s, double alpha, double beta, int depth, boolean jumped){
-
-       if(s.isTerminal() || stop(s, jumped, depth)){
+   private double minValue(CheckersGameState s, double alpha, double beta, int depth, boolean jumped, int min_ply){
+       if(s.isTerminal() || stop(s, jumped, depth, min_ply)){
            return eval.evaluate(s, this.player);
         }
        double v = Double.POSITIVE_INFINITY;
        double check;
        for(Move a: s.actions()){
-           check = maxValue(s.result(a), alpha, beta, depth + 1, a.isJump());
+           check = maxValue(s.result(a), alpha, beta, depth + 1, a.isJump(), min_ply);
            if(check < v){
                v = check;
             }
diff --git a/src/CheckersGameState3.java b/src/CheckersGameState3.java
index 6593464..375f4d2 100644
--- a/src/CheckersGameState3.java
+++ b/src/CheckersGameState3.java
@@ -38,7 +38,7 @@ public class CheckersGameState3 implements CheckersGameState{
 
     boolean canJump(){
         //System.out.println(this.moves);
-        return this.actions.get(0).isJump();
+        return (this.actions.size() > 0 && this.actions.get(0).isJump());
     }
 
     boolean canExchange(){
diff --git a/src/RmCheckersClient.java b/src/RmCheckersClient.java
index 5842136..2b271c8 100644
--- a/src/RmCheckersClient.java
+++ b/src/RmCheckersClient.java
@@ -145,7 +145,7 @@ public class RmCheckersClient {
       }
       while(currentState.actions().size()>0){
         currentState.printState();
-        Move myMove = ai.minimax(currentState);
+        Move myMove = ai.minimax(currentState, 8);
         writeMessageAndEcho(myMove.toString());
         if(!applyMove(myMove.toString())) {
           System.out.println("couldn't apply my move");