Today I have done leetcode's March LeetCoding Challenge with cpp.

March LeetCoding Challenge 5

Description

Count Total Number of Colored Cells

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

class Solution {
public:
  long long coloredCells(int n) {
    return 2LL * (n - 1) * n + 1;
  }
};

// Accepted
// 94/94 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 91.36 % of cpp submissions (7.8 MB)