计算二维列表 python 周围正方形中有多少个符号

Question

I have an assignment in my intro to python course where I have to make a function that goes through a 2d list using loops and when given x and y coordinates it counts how many "N" are in the surrounding squares of the chosen one. x and y can be anywhere and they are not allowed to cross the bounds of the list. For some reason the course material seems very lacking and I can't find anything that will help me get started. How should I go about making the function work?

Paremeters for the function have to be (x, y, the list) The function should assume you are not on an "N" but if you are it counts that one aswell.

If someone can give me some tips on how to get started that would be great.

list = [['N', ' ', ' ', ' ', ' '],
        ['N', 'N', 'N', 'N', ' '],
        ['N', ' ', 'N', ' ', ' '],
        ['N', 'N', 'N', ' ', ' '],
        [' ', ' ', ' ', ' ', ' '],
        [' ', ' ', ' ', ' ', ' ']]

     

Answer 1

From this code you can count how many N in the list:

list_ = [['N', ' ', ' ', ' ', ' '],
        ['N', 'N', 'N', 'N', ' '],
        ['N', ' ', 'N', ' ', ' '],
        ['N', 'N', 'N', ' ', ' '],
        [' ', ' ', ' ', ' ', ' '],
        [' ', ' ', ' ', ' ', ' ']]
count = 0
for a in list_:
    for b in a:
        if b == 'N':
            count += 1
print(count)

Answer 2

From the question it is unclear whether the provided x and y coordinates will be an element around the edge with less than 8 adjacent elements or not.

If the x coordinate had a range of 1 to len(row) - 1 and the y coordinate had a range of 1 to len(column)-1 then you could just loop through each row in the 2d list and then each element in that row and then check if that element is equal to 'N' . This could be solved like so:

def adjacent_count(x, y, list_2d):
    count = 0
    for row in list_2d[x-1:x+2]:
        for element in row[y-1:y+2]:
            if element == 'N':
                count += 1
    return count

Or using list comprehension in one line:

def adjacent_count(x, y, list_2d):
    return sum([1 if element == 'N' else 0 for row in list_2d[x-1:x+2] for element in row[y-1:y+2]])

EDIT: Knowing now that the x and y coordinates can have a range from 0 to len(rows) and len(cols) and that the function should not wrap to the other side of the array the following code can be used. The code now checks to see if the next array element is out of the bounds of the list before trying to access it.

def adjacent_count(x, y, list_2d):
    no_rows, no_cols = len(list_2d), len(list_2d[0])
    count = 0
    for i in range(x-1, x+2):
        for j in range(y-1, y+2):
            if i < no_cols and j < no_rows:
                if list_2d[j][i] == 'N':
                    count += 1
    return count