Day13-Apr-Spiral_Matrix_II

"""
    Problem Link: https://leetcode.com/problems/spiral-matrix-ii/
    Language:
        Python
    Params:
        n: Int
    Return:
        2D intager list
    Complexity Analysis:
        Space: O(nˆ2)
        Time: (nˆ2)
            Outer while loop and inner for loops
            takes (nˆ2) time to execute.
"""

class Solution:
    def generateMatrix(self, n: int) -> List[List[int]]:
        matrix = []
        for _ in range(n):
            matrix.append([0]*n)
        left, right, up, down = 0, n-1, 0, n-1
        curr_num = 0
        while curr_num < n*n:

            for curr_index in range(left, right+1):
                curr_num += 1
                matrix[left][curr_index] = curr_num

            for curr_index in range(up+1, down+1):
                curr_num += 1
                matrix[curr_index][right] = curr_num


            for curr_index in range(right-1, left-1, -1):
                curr_num += 1
                matrix[down][curr_index] = curr_num

            for curr_index in range(down-1, up, -1):
                curr_num += 1
                matrix[curr_index][left] = curr_num

            left += 1
            right -= 1
            up += 1
            down -= 1

        return matrix