54. Spiral Matrix

 

Decription:

https://leetcode.com/problems/spiral-matrix/

We are gonna make the variable name "Top, bottom, right_col, left_col to point the row and column you are currently in. 

Solution:

Solution for sprial matrix

We set the top and bottom to point to the first row and the last row.

Next, we set left_column and right_column to point to the first column and the last column. 

We can see the sprial matrix gets value following this order: top row --> right most column --> bottom row --> left most column.

 

First loop(top row): 

example 1)

from matrix[top][0] to matrix[top][2], so the range should be range(left_col, right_col) --> (0 <= i < 3)

 

Second loop(right most column):

example 1)

from matrix[1][right_col] to matrix[2][right_col], so the range should be range(top, bottom) --> (1 <= i < 3)

 

Third loop(bottom row):

example 1)

from matrix[bottom - 1(2)][1] to matrix[bottom -1(2)][0],

so the range should be range(right_col - 1, left_col -1, -1)  --> (1 >= i > -1)

 

Fourth loop(left most column):

example 1)

just matrix[1][left_col]

so the range should be range(bottom-1, top-1, -1)  --> (1 >= i  > 0)

 

And we return the result. Then, let's talk about the break between the second and third loop.

In case2, we can see the the result list is [1, 2, 3, 4, 8, 12, 11, 10, 9, 5, 6, 7, 6] without the break.

The third loop works twice, and it puts the 6 again.

6 should be the duplication number, because we put 6 after the seond time of first loop.

So, that's why we should put the break on our codes.

 

Time complexity O(m*n)

Space complexity: O(1)