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

January LeetCoding Challenge 26

Description

Out of Boundary Paths

There is an m x n grid with a ball. The ball is initially at the position [startRow, startColumn]. You are allowed to move the ball to one of the four adjacent cells in the grid (possibly out of the grid crossing the grid boundary). You can apply at most maxMove moves to the ball.

Given the five integers m, n, maxMove, startRow, startColumn, return the number of paths to move the ball out of the grid boundary. Since the answer can be very large, return it modulo 109 + 7.

Example 1:

Input: m = 2, n = 2, maxMove = 2, startRow = 0, startColumn = 0
Output: 6

Example 2:

Input: m = 1, n = 3, maxMove = 3, startRow = 0, startColumn = 1
Output: 12

Constraints:

• 1 <= m, n <= 50
• 0 <= maxMove <= 50
• 0 <= startRow < m
• 0 <= startColumn < n

Solution

const int SZ = 50;
const int MOD = 1e9 + 7;
int path[2][SZ][SZ];
const int moves[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
class Solution {
public:
  int findPaths(int m, int n, int maxMove, int startRow, int startColumn) {
    memset(path[0], 0, sizeof(path[0]));
    path[0][startRow][startColumn] = 1;
    int result = 0;
    for(int cnt = 0; cnt < maxMove; cnt++) {
      int parity = cnt & 1;
      memset(path[!parity], 0, sizeof(path[0]));
      for(int i = 0; i < m; ++i) {
        for(int j = 0; j < n; ++j) {
          // cout << path[parity][i][j] << ' ' ;
          for(int c = 0; c < 4; ++c) {
            int newRow = i + moves[c][0];
            int newCol = j + moves[c][1];
            if(newRow < 0 || newCol < 0 || newRow >= m || newCol >= n) continue;
            path[!parity][newRow][newCol] += path[parity][i][j];
            path[!parity][newRow][newCol] %= MOD;
          }
        }
        // cout << endl;
      }
      // cout << endl;
      for(int i = 0; i < m; ++i) {
        result += path[parity][i][0];
        result %= MOD;
        result += path[parity][i][n - 1];
        result %= MOD;
      }
      for(int i = 0; i < n; ++i) {
        result += path[parity][0][i];
        result %= MOD;
        result += path[parity][m - 1][i];
        result %= MOD;
      }
    }
    return result;
  }
};

// Accepted
// 94/94 cases passed (8 ms)
// Your runtime beats 84.71 % of cpp submissions
// Your memory usage beats 100 % of cpp submissions (5.8 MB)