Given width = 3, height = 2, and food = [[1,2],[0,1]].

Snake snake = new Snake(width, height, food);

Initially the snake appears at position (0,0) and the food at (1,2).

|S| | |
| | |F|

snake.move("R"); -> Returns 0

| |S| |
| | |F|

snake.move("D"); -> Returns 0

| | | |
| |S|F|

snake.move("R"); -> Returns 1 (Snake eats the first food and right after that, the second food appears at (0,1) )

| |F| |
| |S|S|

snake.move("U"); -> Returns 1

| |F|S|
| | |S|

snake.move("L"); -> Returns 2 (Snake eats the second food)

| |S|S|
| | |S|

snake.move("U"); -> Returns -1 (Game over because snake collides with border)

class SnakeGame {
public:
    /** Initialize your data structure here.
        @param width - screen width
        @param height - screen height 
        @param food - A list of food positions
        E.g food = [[1,1], [1,0]] means the first food is positioned at [1,1], the second is at [1,0]. */
    SnakeGame(int width, int height, vector<pair<int, int>> food) {
        this->width = width;
        this->height = height;
        this->food = food;
        score = 0;
        snake.push_back({0, 0});
    }
    
    /** Moves the snake.
        @param direction - 'U' = Up, 'L' = Left, 'R' = Right, 'D' = Down 
        @return The game's score after the move. Return -1 if game over. 
        Game over when snake crosses the screen boundary or bites its body. */
    int move(string direction) {
        auto head = snake.front(), tail = snake.back();
        snake.pop_back();
        if (direction == "U") --head.first;
        else if (direction == "L") --head.second;
        else if (direction == "R") ++head.second;
        else if (direction == "D") ++head.first;
        if (count(snake.begin(), snake.end(), head) || head.first < 0 || head.first >= height || head.second < 0 || head.second >= width) {
            return -1;
        }
        snake.insert(snake.begin(), head);
        if (!food.empty() && head == food.front()) {
            food.erase(food.begin());
            snake.push_back(tail);
            ++score;
        }
        return score;
    }

private:
    int width, height, score;
    vector<pair<int, int>> food, snake;
};