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

November LeetCoding Challenge 1

Description

Where Will the Ball Fall

You have a 2-D grid of size m x n representing a box, and you have n balls. The box is open on the top and bottom sides.

Each cell in the box has a diagonal board spanning two corners of the cell that can redirect a ball to the right or to the left.

A board that redirects the ball to the right spans the top-left corner to the bottom-right corner and is represented in the grid as 1.
A board that redirects the ball to the left spans the top-right corner to the bottom-left corner and is represented in the grid as -1.

We drop one ball at the top of each column of the box. Each ball can get stuck in the box or fall out of the bottom. A ball gets stuck if it hits a "V" shaped pattern between two boards or if a board redirects the ball into either wall of the box.

Return an array answer of size n where answer[i] is the column that the ball falls out of at the bottom after dropping the ball from the i^th column at the top, or -1 if the ball gets stuck in the box.

Example 1:

Input: grid = [[1,1,1,-1,-1],[1,1,1,-1,-1],[-1,-1,-1,1,1],[1,1,1,1,-1],[-1,-1,-1,-1,-1]]
Output: [1,-1,-1,-1,-1]
Explanation: This example is shown in the photo.
Ball b0 is dropped at column 0 and falls out of the box at column 1.
Ball b1 is dropped at column 1 and will get stuck in the box between column 2 and 3 and row 1.
Ball b2 is dropped at column 2 and will get stuck on the box between column 2 and 3 and row 0.
Ball b3 is dropped at column 3 and will get stuck on the box between column 2 and 3 and row 0.
Ball b4 is dropped at column 4 and will get stuck on the box between column 2 and 3 and row 1.

Example 2:

Input: grid = [[-1]]
Output: [-1]
Explanation: The ball gets stuck against the left wall.

Example 3:

Input: grid = [[1,1,1,1,1,1],[-1,-1,-1,-1,-1,-1],[1,1,1,1,1,1],[-1,-1,-1,-1,-1,-1]]
Output: [0,1,2,3,4,-1]

Constraints:

m == grid.length
n == grid[i].length
1 <= m, n <= 100
grid[i][j] is 1 or -1.

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  vector<int> findBall(vector<vector<int>>& grid) {
    int rows = grid.size();
    int cols = grid.front().size();
    if(cols == 1) return { -1 };
    vector<vector<int>> result(2, vector<int>(cols));
    for(int i = 0; i < cols; ++i) {
      result[rows & 1][i] = i;
    }
    for(int row = rows - 1; row >= 0; --row) {
      int curRow = row & 1;
      for(int j = 1; j < cols - 1; ++j) {
        if(grid[row][j] == grid[row][j + grid[row][j]]) {
          result[curRow][j] = result[curRow ^ 1][j + grid[row][j]];
        } else {
          result[curRow][j] = -1;
        }
      }
      if(grid[row][0] == -1 || grid[row][1] != grid[row][0]) {
        result[curRow][0] = -1;
      } else {
        result[curRow][0] = result[curRow ^ 1][1];
      }
      if(grid[row][cols - 1] == 1 || grid[row][cols - 1] != grid[row][cols - 2]) {
        result[curRow][cols - 1] = -1;
      } else {
        result[curRow][cols - 1] = result[curRow ^ 1][cols - 2];
      }
    }
    return result[0];
  }
};

// Accepted
// 64/64 cases passed (48 ms)
// Your runtime beats 65.19 % of cpp submissions
// Your memory usage beats 19.11 % of cpp submissions (13.3 MB)

2022-11-01 Daily Challenge

November LeetCoding Challenge 1

Description

Solution