Add more solutions and fix some casual mistakes

* The new added problems' number to the medium level are:
  46, 50, 55, 56, 67, 70.
* The new added problems' number to the easy level are:
  31, 40, 41, 49, 51, 52, 66, 83, 88, 90, 99, 120, 143, 166.
* Change the ID of the problem "Infix Calculator" from 134 to 135.
* Move the problem 122 to the right place (after Pro.120 and before
  Pro.122).