动态规划_leetcode416

# coding=utf8


# 递归
class Solution1(object):
 def combinationSum4(self, nums, target):
 """
 :type nums: List[int]
 :type target: int
 :rtype: int
 """

 if not nums or target <= 0:
 return 0

 return self.tryCombination(nums,target)


 #组合遍历
 def tryCombination(self,nums,target):

 if target == 0:
 return 1

 res = 0
 for item in nums:
 if target - item >= 0:
 res += self.tryCombination(nums,target-item)


 return res



# s = Solution1()
#
# nums = [1,2,3]
# target = 4
#
#
# print s.combinationSum4(nums,target)


# 记忆化递归
class Solution2(object):
 def combinationSum4(self, nums, target):
 """
 :type nums: List[int]
 :type target: int
 :rtype: int
 """

 if not nums or target <= 0:
 return 0



 self.memo = [-1 for i in range(target+1)]

 return self.tryCombination(nums,target)



 def tryCombination(self,nums,target):


 if self.memo[target] != -1:
 return self.memo[target]

 # self.memo[0] -1
 if target == 0:
 return 1

 res = 0
 for item in nums:
 if target - item >= 0:
 res += self.tryCombination(nums,target-item)

 self.memo[target] = res

 return res


# s = Solution2()
#
# nums = [1,2,3]
# target = 4
#
#
# print s.combinationSum4(nums,target)


# 动态规划
class Solution3(object):
 def combinationSum4(self, nums, target):
 """
 :type nums: List[int]
 :type target: int
 :rtype: int
 """

 if not nums or target <= 0:
 return 0

 memo = [-1 for i in range(target+1)]

 memo[0] = 1

 for i in range(1,target+1):
 memo[i] = 0
 for item in nums:
 if i - item >= 0:
 memo[i] += memo[i-item]


 return memo[target]


s = Solution3()

nums = [1,2,3]
target = 4


print s.combinationSum4(nums,target)