Python Notebook Solution (beat over 99.3%)

  • 0
    def combinationSum4(self, nums, target):
            :type nums: List[int]
            :type target: int
            :rtype: int
            solution = {}
            def findSum4(Sum):
                result = solution.get(Sum, -1)
                if(result >= 0):
                    return result
                result = 0
                for i in nums:
                    if(i < Sum):
                        result += findSum4(Sum - i)
                    elif(i == Sum):
                        result += 1
                solution[Sum] = result
                return result
            if((not nums) or target <= 0):
                return 0
            return findSum4(target)

    recursive solution suffered TLE
    DP solution must calculate a lot of undesired subproblems
    In this case, sum for a certain subproblem can serve as the key for the recursive function to search for an available solution in the dictionary(notebook). Since the key is an integer, the search of a hash table is rather low. And notebook solution does not have to calculate undesired subproblems.
    So recursive and DP are not the best solution for this problem.

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