modify code

Author: algorithmzuo

src/class43/Code03_PavingTile.java

@@ -148,7 +148,7 @@ public static int dfs3(int op, int col, int level, int N, int M, int[][] dp) {
 }
 int ans = 0;
 ans += dfs3(op, col - 1, level, N, M, dp);
-if ((op & (1 << col)) == 0 && col - 1 >= 0 && (op & (1 << (col - 1))) == 0) {
+if (col > 0 && (op & (3 << (col - 1))) == 0) {
 ans += dfs3((op | (3 << (col - 1))), col - 2, level, N, M, dp);
 }
 return ans;