̶Y̶o̶u̶ ̶s̶h̶o̶u̶l̶d̶n̶'̶t̶ ̶u̶s̶e̶ ̶m̶a̶p̶ ̶h̶e̶r̶e̶ ̶b̶e̶c̶a̶u̶s̶e̶ ̶i̶n̶ ̶y̶o̶u̶r̶ ̶c̶o̶d̶e̶ ̶i̶t̶ ̶s̶t̶o̶r̶e̶s̶ ̶t̶o̶o̶ ̶m̶a̶n̶y̶ ̶e̶l̶e̶m̶e̶n̶t̶s̶.̶ ̶T̶h̶e̶ ̶m̶a̶x̶i̶m̶u̶m̶ ̶a̶l̶l̶o̶w̶e̶d̶ ̶n̶u̶m̶b̶e̶r̶ ̶o̶f̶ ̶i̶n̶d̶i̶c̶e̶s̶ ̶i̶s̶ ̶a̶b̶o̶u̶t̶ ̶1̶0̶^̶7̶,̶ ̶b̶u̶t̶ ̶y̶o̶u̶ ̶s̶t̶o̶r̶e̶ ̶1̶0̶^̶1̶8̶ ̶e̶l̶e̶m̶e̶n̶t̶s̶!̶ ̶I̶t̶'̶s̶ ̶i̶m̶p̶o̶s̶s̶i̶b̶l̶e̶ ̶f̶o̶r̶ ̶a̶ ̶s̶i̶n̶g̶l̶e̶ ̶P̶C̶ ̶h̶o̶l̶d̶ ̶s̶u̶c̶h̶ ̶a̶ ̶h̶u̶g̶e̶ ̶a̶m̶o̶u̶n̶t̶ ̶o̶f̶ ̶m̶e̶m̶o̶r̶y̶!̶

Sorry, I'm wrong. You should, in fact, use map, but the problem is with your dfs function. It seems that the map and the function are called too many times, which results in MLE.