diff --git a/main.cpp b/main.cpp
index e65fd86..114b0f8 100644
--- a/main.cpp
+++ b/main.cpp
@@ -210,8 +210,8 @@ void printScores(int *points) {
     dealloc(arr);
 }
 
-bool isValidMove(int x, int y) {
-    return (x & 1) != (y & 1);
+bool isValidMove(int x, int y, char **board) {
+    return (x & 1) != (y & 1) && board[x][y] == ' ';
 }
 
 void addPoint(
@@ -310,7 +310,7 @@ void solve(Moves moves, char **board) {
         int moveY = move.moveY;
         char player = move.player;
 
-        if (!isValidMove(moveX, moveY)) {
+        if (!isValidMove(moveX, moveY, board)) {
             pt "Invalid move by: " << player << " at (x, y): (" << moveX << ", " << moveY << ")" << nl;
             board[moveX][moveY] = 'X';
             printBoard(board, moves.x, moves.y);
@@ -323,9 +323,9 @@ void solve(Moves moves, char **board) {
         board[moveX][moveY] = toLowerCase(player);
 
         // TODO:
-        if (moveX % 2 == 0 && moveY % 2 == 1) {
+        if (!(moveX&1) && (moveY&1)) {
             solveVertical(moveX, moveY, board, points, moves.x, moves.y, player);
-        } else if (moveX % 2 == 1 && moveY % 2 == 0) {
+        } else if ((moveX&1) && !(moveY&1)) {
             solveHorizontal(moveX, moveY, board, points, moves.y, player);
         } else {
             pt "Invalid move by: " << player << " at (x, y): (" << moveX << ", " << moveY << ")" << nl;