如何使用python查找矩阵中平方的最大和

Question

I am trying to write a code that will give me the biggest sum of a square in a matrix.

note: the values have to be next to each other while forming the shape of a square.

note 2: I am only allowed to use functions, importing anything isn't allowed currently in the class I am taking.

For example:

 max_mat_square([[1,2.5,3],
                 [4,-4,6],
                 [0.5,-1,5]])

[7.5]

Now this is the code I have:

def max_mat_square(mat):
    sum1 = []
    for i in range(len(mat[:-1])):
        print i
        for j in range(len(mat[1:])):
                print 'index' , j
                sum1.append([float(mat[i][j]) + float(mat[i+1][j])+float(mat[i][j+1])+float(mat[i+1][j+1])])
    return max(sum1)

Now the code works fine with the first example, However whenever I run this matrix throw it:

max_mat_square([[1,2], [3,4], [5,6]])

I get 'list index out of range' error, The result I want for this matrix is 18.

I tried a lot of methods to fix the error, but none of them worked.

Answer 1

The problem is your inner for loop. You should have j starting from 0 up to the row's second last index:

for j in range(len(mat[i][:-1])):
    ...

So your final function becomes:

def max_mat_square(mat):
    sum1 = []
    for i in range(len(mat[:-1])):
        print(i)
        for j in range(len(mat[i][:-1])):
                print('index' , j)
                sum1.append([float(mat[i][j]) + float(mat[i+1][j])+float(mat[i][j+1])+float(mat[i+1][j+1])])
    return max(sum1)

Answer 2

I think your first example works only co-incidentally because of the shape of your matrix. Currently the slicing used in that loop means you are selecting from the second sub-list to the end:

mat[1:]
>> [[3,4], [5,6]]

Which implies you'll try to loop through each element with range(2) which will go out of range.

Change the second for statement as follows:

def max_mat_square(mat):
    sum1 = []
    for i in range(len(mat[:-1])):
        for j in range(len(mat[i])-1):
            print (i , j)
            sum1.append([float(mat[i][j]) + float(mat[i+1][j])+float(mat[i][j+1])+float(mat[i+1][j+1])])
    return max(sum1)