func uniquePaths(m int, n int) int {
  dp := make([][]int, m)
  for i := range dp {
      dp[i] = make([]int, n)
  }

  for i := 0; i < m; i++ {
    for j := 0; j < n; j++ {
      if i == 0 || j == 0 {
        dp[i][j] = 1
      } else {
        dp[i][j] = dp[i-1][j] + dp[i][j-1]
      }
    }
  }
  return dp[m-1][n-1]
}