tmp

q.cpp

[In Haskell]

    foldr :: (a -> b -> b) -> b -> [a] -> b
    foldr = ......

    (example)

    foldr (+) 0 [a,b,c] = a + (b + (c + 0))

[In C++]

    typedef B (*fun_a_b_to_b)(A, B);

    B foldr(fun_a_b_to_b func, B zero, const vector<A> &array) {
        B answer = zero;
        for (i = array.size() - 1; i >= 0; i--) {
            answer = func(array[i], answer);
        }
        return answer;
    }

    (example)

    // A = int
    // B = int

    int add(int a, int b) {
        return (a + b);
    }

    vector<int> array = {3, 5, 7};

    int result = foldr(add, 0, array);
    // result = 3 + (5 + (7 + 0))

q2.cpp

    // If your task were in C++...
    
    struct Result {
        // blah
    };
    struct Attack {
        char attack_column;
        int  attack_row;
    };

    Result attackOne(Attack a, Result board) {
        // blah
    }
    
    Result ships(Result board, vector<Attack> array) {
        // Probably you can do it manually,
        // but can you implement it using foldr( , , )?
    }