Snake game

Simulate the Snake game on a grid of given width and height. The snake starts length 1 at (row 0, col 0). Food positions are given in order as [row, col] pairs; the snake eats the next food only when its head lands exactly on it. Given a sequence of moves (each 'U','D','L','R'), return the score (food eaten) after the LAST successfully applied move, or -1 as soon as a move kills the snake (running into a wall or its own body). Eating food grows the snake by 1 (tail does not move that step). The snake's body is its own obstacle except that the tail cell vacates as the head advances (unless it just ate).