can give me sample of test case where this return wrong result? thanks

(hint 1: board[i][j] is uint. what is the value of board[i][j]-1 ? is it equal to -1, or is it equal to something else?)

(hint 2: try to run this code first, edit it and try to print the value of x |= 1 << (board[i][j]-1) to stdout);