Created basic version of game.

app/build.gradle

@@ -6,7 +6,7 @@ android {
 
     defaultConfig {
         applicationId "com.example.jagadeesh545.piczzle"
-        minSdkVersion 9
+        minSdkVersion 11
         targetSdkVersion 23
         versionCode 1
         versionName "1.0"

app/src/main/AndroidManifest.xml

@@ -16,6 +16,7 @@
             </intent-filter>
         </activity>
         <activity android:name=".Game"></activity>
+        <activity android:name=".Victory" ></activity>
     </application>
 
 </manifest>

app/src/main/java/com/example/jagadeesh545/piczzle/Game.java

@@ -1,25 +1,153 @@
 package com.example.jagadeesh545.piczzle;
 
+import android.content.Intent;
 import android.support.v7.app.AppCompatActivity;
 import android.os.Bundle;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.Button;
 
+import java.util.Arrays;
+import java.util.Collections;
+
 public class Game extends AppCompatActivity {
+    Integer[] numbers = new Integer[15];
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_game);
-        ViewGroup game_view = (ViewGroup) findViewById(R.id.game_view);
-        int block_height = game_view.getHeight()/4;
-        int block_width = game_view.getWidth()/4;
-        for (int i = 0; i < game_view.getChildCount(); i++) {
-            Button current_button = (Button) game_view.getChildAt(i);
-            current_button.setHeight(block_height);
-            current_button.setWidth(block_width);
-            current_button.setText(String.valueOf(i));
+
+        for (int i = 0; i < numbers.length; i++) {
+            numbers[i] = i+1;
+        }
+        Collections.shuffle(Arrays.asList(numbers));
+        if(!checkSolvable(numbers)){
+            int temp = numbers[0];
+            numbers[0] = numbers[1];
+            numbers[1] = temp;
+        }
+
+        final View game_view = findViewById(R.id.game_view);
+        final ViewGroup game_viewGroup = (ViewGroup) findViewById(R.id.game_view);
+        game_view.post(new Runnable() {
+            @Override
+            public void run() {
+                int block_width = game_view.getWidth() / 4;
+                int block_height = game_view.getHeight() / 4;
+                if (block_height > 0 && block_width > 0) {
+                    for (int i = 0; i < game_viewGroup.getChildCount(); i++) {
+                        Button current_button = (Button) game_viewGroup.getChildAt(i);
+                        ViewGroup.LayoutParams params = current_button.getLayoutParams();
+                        params.height = block_height;
+                        params.width = block_width;
+                        current_button.setLayoutParams(params);
+                        current_button.setTextSize((float) (block_height * 0.10));
+                        current_button.setOnClickListener(new View.OnClickListener() {
+                            @Override
+                            public void onClick(View v) {
+                                swap(v);
+                            }
+                        });
+                    }
+                }
+            }
+        });
+
+        int last = game_viewGroup.getChildCount() - 1;
+        Button current_button = (Button) game_viewGroup.getChildAt(last);
+        current_button.setText("*");
+        for (int i = 0; i < last; i++) {
+            Button temp_button = (Button) game_viewGroup.getChildAt(i);
+            temp_button.setText(String.valueOf(numbers[i]));
+        }
+    }
+
+    // Check if the puzzle is solvable
+    public boolean checkSolvable(Integer[] numbers) {
+        int inversions = 0;
+
+        for(int i = 0; i < numbers.length; i++) {
+            for(int j = i+1; j < numbers.length; j++) {
+                if(numbers[j] > numbers[i]){
+                    inversions++;
+                }
+            }
+        }
+
+        if(inversions%2 == 1){
+            return false;
+        }
+
+        return true;
+    }
+
+    // Swap the blocks if they are adjacent to blank block
+    public void swap(View view) {
+        if(view.getId() == R.id.blank) {
+            return;
+        }
+        View blank = findViewById(R.id.blank);
+        int block_height = blank.getHeight();
+        int block_width = blank.getWidth();
+        if((blank.getX()-view.getX()==block_width && blank.getY()-view.getY()==0)||
+                (blank.getX()-view.getX()==-block_width && blank.getY()-view.getY()==0)||
+                (blank.getX()-view.getX()==0 && blank.getY()-view.getY()==block_height)||
+                (blank.getX()-view.getX()==0 && blank.getY()-view.getY()==-block_height))
+        {
+            swapBlocks(view);
+            checkBoard();
+        }
+    }
+
+    // Perform actual swap operation
+    public void swapBlocks(View view) {
+
+        float viewX = view.getX();
+        float viewY = view.getY();
+
+        View blank = findViewById(R.id.blank);
+        float blankX = blank.getX();
+        float blankY = blank.getY();
+
+        blank.setX(viewX);
+        blank.setY(viewY);
+
+        view.setX(blankX);
+        view.setY(blankY);
+    }
+
+    // Check board to see if the puzzle is solved.
+    public void checkBoard() {
+        View blank = findViewById(R.id.blank);
+        int block_height = blank.getHeight();
+        int block_width = blank.getWidth();
+        ViewGroup game_viewGroup = (ViewGroup) findViewById(R.id.game_view);
+        for (int i = 0; i < game_viewGroup.getChildCount() - 1; i++) {
+            Button current_button = (Button) game_viewGroup.getChildAt(i);
+            int current_value = Integer.valueOf(String.valueOf(current_button.getText())) - 1;
+            int a = (int) current_button.getX() / block_width;
+            int b = current_value % 4;
+            int c = (int) current_button.getY() / block_height;
+            int d = current_value / 4;
+            if (a != b || c != d) {
+                return;
+            }
+        }
+        int last = game_viewGroup.getChildCount() - 1;
+        Button current_button = (Button) game_viewGroup.getChildAt(last);
+        if(String.valueOf(current_button.getText()).compareTo("*")!=0) {
+            return;
+        }
+        else {
+            current_button.setText(String.valueOf(last+1));
+        }
+
+        for (int i = 0; i < game_viewGroup.getChildCount(); i++) {
+            Button temp_button = (Button) game_viewGroup.getChildAt(i);
+            temp_button.setClickable(false);
         }
+        Intent intent = new Intent(this, Victory.class);
+        startActivity(intent);
     }
 }

app/src/main/java/com/example/jagadeesh545/piczzle/MainActivity.java

@@ -1,37 +1,20 @@
 package com.example.jagadeesh545.piczzle;
 
+import android.content.Intent;
 import android.support.v7.app.AppCompatActivity;
 import android.os.Bundle;
 import android.view.View;
-import android.view.ViewGroup;
-import android.widget.Button;
 
 public class MainActivity extends AppCompatActivity {
-
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
-        setContentView(R.layout.activity_game);
+        setContentView(R.layout.activity_main);
+    }
 
-        final View game_view = findViewById(R.id.game_view);
-        game_view.post(new Runnable() {
-            @Override
-            public void run() {
-                int block_width = game_view.getWidth()/4;
-                int block_height = game_view.getHeight()/4;
-                if (block_height > 0 && block_width > 0) {
-                    ViewGroup game_viewGroup = (ViewGroup) findViewById(R.id.game_view);
-                    for (int i = 0; i < game_viewGroup.getChildCount(); i++) {
-                        Button current_button = (Button) game_viewGroup.getChildAt(i);
-                        ViewGroup.LayoutParams params = current_button.getLayoutParams();
-                        params.height = block_height;
-                        params.width = block_width;
-                        current_button.setLayoutParams(params);
-                        current_button.setText(String.valueOf(i + 1));
-                        current_button.setTextSize((float)(block_height * 0.10));
-                    }
-                }
-            }
-        });
+    /** Launches game activity */
+    public void launchGame(View view) {
+        Intent intent = new Intent(this, Game.class);
+        startActivity(intent);
     }
 }

app/src/main/java/com/example/jagadeesh545/piczzle/Victory.java

@@ -0,0 +1,13 @@
+package com.example.jagadeesh545.piczzle;
+
+import android.support.v7.app.AppCompatActivity;
+import android.os.Bundle;
+
+public class Victory extends AppCompatActivity {
+
+    @Override
+    protected void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.activity_victory);
+    }
+}

app/src/main/res/layout/activity_game.xml

@@ -118,7 +118,7 @@
     <Button
         android:layout_width="40dp"
         android:layout_height="40dp"
-        android:id="@+id/button16"
+        android:id="@+id/blank"
         android:layout_below="@+id/button12"
         android:layout_toRightOf="@+id/button15" />
 

app/src/main/res/layout/activity_main.xml

@@ -9,8 +9,12 @@
     android:paddingTop="@dimen/activity_vertical_margin"
     tools:context="com.example.jagadeesh545.piczzle.MainActivity">
 
-    <TextView
+    <Button
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
-        android:text="Hello World!" />
+        android:text="Click to Start!"
+        android:id="@+id/button"
+        android:layout_centerVertical="true"
+        android:layout_centerHorizontal="true"
+        android:onClick="launchGame"/>
 </RelativeLayout>

app/src/main/res/layout/activity_victory.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:paddingBottom="@dimen/activity_vertical_margin"
+    android:paddingLeft="@dimen/activity_horizontal_margin"
+    android:paddingRight="@dimen/activity_horizontal_margin"
+    android:paddingTop="@dimen/activity_vertical_margin"
+    tools:context="com.example.jagadeesh545.piczzle.Victory">
+
+    <TextView
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:text="Congratulations!! You Win!!"
+        android:id="@+id/textView"
+        android:layout_centerVertical="true"
+        android:layout_centerHorizontal="true" />
+</RelativeLayout>