[Leetcode][Python]39: Combination Sum

# -*- coding: utf8 -*-‘‘‘__author__ = ‘[email protected]‘

39: Combination Sumhttps://oj.leetcode.com/problems/combination-sum/

Given a set of candidate numbers (C) and a target number (T),find all unique combinations in C where the candidate numbers sums to T.The same repeated number may be chosen from C unlimited number of times.

Note:All numbers (including target) will be positive integers.Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).The solution set must not contain duplicate combinations.For example, given candidate set 2,3,6,7 and target 7,A solution set is:[7][2, 2, 3]

===Comments by Dabay===递归。先把candidates排序。遍历candidates，用index来记录目前的指针。‘‘‘

class Solution:    # @param candidates, a list of integers    # @param target, integer    # @return a list of lists of integers    def combinationSum(self, candidates, target):        def combinationSum2(candidates, target, index, res, res_list):            if target == 0:                res_list.append(list(res))                return            while index < len(candidates) and target >= candidates[index]:                res.append(candidates[index])                combinationSum2(candidates, target-candidates[index], index, res, res_list)                res.pop()                index += 1

        res_list = []        candidates.sort()        combinationSum2(candidates, target, 0, [], res_list)        return res_list

def main():    sol = Solution()    candidates = [1,2]    target = 4    print sol.combinationSum(candidates, target)

if __name__ == "__main__":    import time    start = time.clock()    main()    print "%s sec" % (time.clock() - start)