## Issue

I have to make a matrix thats N by N and the example im given looks like this:

```
4 0 0 0
3 3 0 0
2 2 2 0
1 1 1 1
```

So what I get from the example is that its gonna take the number N is (4 in this example since its 4 by 4) and print the number on the top row first column then fill it with zeros and then go down one line and print N -1 in the first two columns and then zeros.

My code looks like this atm:

```
def fill_matrix(n): #Fills the matrix with 0s
# Llena la matriz
for r in range(n):
row = []
for c in range(n):
row.append(0)
matrix.append(fila)
return matrix
def print_matrix(matriz): #Prints the matrix
rows = len(matriz)
columns = len(matriz[0])
for f in range(row):
for c in range(columns):
print ("%3d" %matrix[f][c], end="")
print()
# Programa principal
side = int(input("Input the size of the matrix: ")) #Input of N by N
while side < 1:
print("Size must be bigger than 0")
side = int(input("Input the size of the matrix: "))
matrix = []
fill_matrix(side)
print_matrix(matrix)
```

How can I make this matrix look like the one in the exercise?

## Solution

Use list comprehension:

```
N = 4
>>> [[N-i]*(i+1)+[0]*(N-i-1) for i in range(N)]
[[4, 0, 0, 0], [3, 3, 0, 0], [2, 2, 2, 0], [1, 1, 1, 1]]
```

In a function:

```
def fill_matrix(N):
return [[N-i]*(i+1)+[0]*(N-i-1) for i in range(N)]
def print_matrix(m):
print("\n".join(["\t".join(map(str, row)) for row in m]))
>>> fill_matrix(6)
[[6, 0, 0, 0, 0, 0],
[5, 5, 0, 0, 0, 0],
[4, 4, 4, 0, 0, 0],
[3, 3, 3, 3, 0, 0],
[2, 2, 2, 2, 2, 0],
[1, 1, 1, 1, 1, 1]]
>>> print_matrix(fill_matrix(6))
6 0 0 0 0 0
5 5 0 0 0 0
4 4 4 0 0 0
3 3 3 3 0 0
2 2 2 2 2 0
1 1 1 1 1 1
```

The ith row consists of:

- The number N-i repeated i+1 times
- 0 repeated N-(i+1) times

Answered By – not_speshal

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