Description
There exists an infinitely large two-dimensional grid of uncolored unit cells. You are given a positive integer n, indicating that you must do the following routine for n minutes:
- At the first minute, color any arbitrary unit cell blue.
- Every minute thereafter, color blue every uncolored cell that touches a blue cell.
Below is a pictorial representation of the state of the grid after minutes 1, 2, and 3.
Return the number of colored cells at the end of n minutes.
Example 1:
Input: n = 1 Output: 1 Explanation: After 1 minute, there is only 1 blue cell, so we return 1.
Example 2:
Input: n = 2 Output: 5 Explanation: After 2 minutes, there are 4 colored cells on the boundary and 1 in the center, so we return 5.
Constraints:
1 <= n <= 105
Solution
Python3
class Solution:
def coloredCells(self, n: int) -> int:
# 4, 8, 12
# 1, 5, 13, 25
m = 4
curr = 1
for _ in range(n - 1):
curr += m
m += 4
return curr