动态规划_leetcode91

#coding=utf-8
class Solution1(object):
    def numDecodings(self, s):
        """
 :type s: str
 :rtype: int

 """
 if not s:
 return

 return self.decode(s)

 pass

 def decode(self,s):


 if len(s) == 0:
 return 1

 if len(s) == 1:
 num = int(s[0])

 if num >= 1 and num <= 26:
 return 1

 return 0



 res = 0
 num1 = int(s[0])

 if num1 >= 1 and num1 <= 26:
 res += self.decode(s[1:])
 else:
 return res

 num2 = int(s[0:2])

 if num2 >= 1 and num2 <= 26:
 res += self.decode(s[2:])

 return res




# s = Solution1()
#
# ts = "4757562545844617494555774581341211511296816786586787755257741178599337186486723247528324612117156948"
#
# print s.numDecodings(ts)


# 记忆化递归不太好记录状态,直接使用动归
# key 为数组确实不太好记状态 20190306
class Solution3(object):
 def numDecodings(self, s):
 """
 :type s: str
 :rtype: int

 """
 if not s:
 return

 return self.decode(s)



 def decode(self,s):

 length = len(s)

 if length == 1:
 num = int(s[0])

 if num >= 1 and num <= 26:
 return 1

 return 0

 memo = [0 for i in range(length+1)]

 num1 = int(s[length-1])

 memo[length] = 1

 if num1 == 0:
 memo[length-1] = 0
 else:
 memo[length-1] = 1


 for i in range(length-2,-1,-1):

 num1 = int(s[i])

 if num1 == 0:
 memo[i] = 0
 continue

 num2 = int(s[i:i+2])

 if num2 >= 10 and num2 <= 26:
 memo[i] = memo[i+1]+ memo[i+2]
 else:
 memo[i] = memo[i+1]


 return memo[0]


s = Solution3()

print s.numDecodings("12")