unique_paths.py

class Solution:
    def uniquePaths(self, m: int, n: int) -> int:
        grid = [[1] * n for _ in range(m)]
        for i in range(1, m):
            for j in range(1, n):
                grid[i][j] = grid[i - 1][j] + grid[i][j - 1]
                
        return grid[-1][-1]