fix word ladder issue for python
fix word ladder issue for python

Signed-off-by: Peng Xiao <dc8b7d6a85c199a18f82ef7727e6dbbbae446be2@gmail.com>

tudennis/LeetCode---kamyu104-11-24-2015,tudennis/LeetCode---kamyu104-11-24-2015,tudennis/LeetCode---kamyu104-11-24-2015,tudennis/LeetCode---kamyu104-11-24-2015,kamyu104/LeetCode,kamyu104/LeetCode,kamyu104/LeetCode,jaredkoontz/leetcode,kamyu104/LeetCode,jaredkoontz/leetcode,yiwen-luo/LeetCode,yiwen-luo/LeetCode,yiwen-luo/LeetCode,yiwen-luo/LeetCode,yiwen-luo/LeetCode,kamyu104/LeetCode,jaredkoontz/leetcode,tudennis/LeetCode---kamyu104-11-24-2015,jaredkoontz/leetcode,jaredkoontz/leetcode