动态规划_leetcode91
Posted AceKo
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#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")
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Leetcode 91. Decode Ways 解码方法(动态规划，字符串处理)