code: def combination_memo(n, r):
      """This function calculates nCr using memoization method."""
      memo = {}
  
      def recur(n, r):
          if n == r or r == 0:
              return 1
          if (n, r) not in memo:
              memo[(n, r)] = recur(n - 1, r - 1) + recur(n - 1, r)
          return memo[(n, r)]
  
      return recur(n, r)
  
label_desc: Use image node_id 2 for calling a global function with example usage: combination_memo(n, r) and returns: recur, memo, int