new_contents: class Solution:
      # @param start, a string
      # @param end, a string
      # @param dict, a set of string
      # @return an integer
      def ladderLength(self, start, end, dict):
          # write your code here
          queue = [start]
          level = 1
          levelIndex = 0
          dict.add(end)
          while (queue):
              currentStr = queue.pop(0)
              if (currentStr == end):
                  return level
              i = 0
              while (i < len(currentStr)):
                  for j in range(97, 123):
                      tmp = currentStr[:i] + chr(j) + currentStr[i+1:]
                      if (tmp in dict):
                          queue.append(tmp)
                          dict.remove(tmp)
                  i += 1
              levelIndex -= 1
              if (levelIndex <= 0):
                  level += 1
                  levelIndex = len(queue)
          return 0
  
subject: Add solution to lintcode question 120