new_contents: 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] 
  
  class Solution:
      # @param candidates, a list of integers
      # @param target, integer
      # @return a list of lists of integers
      
      # Recursion
      # Sort the array at first, then use the recursion to find 
      # the result, Time O(n^2)
      # 96ms
      def combinationSum(self, candidates, target):
          candidates.sort()
          self.result = []
          self.dfs(candidates,target,0,[])
          return self.result 
          
      def dfs(self,candidates,target,start,reslist):
          length = len(candidates)
          if target == 0: 
              return self.result.append(reslist)
          
          for i in xrange(start,length):
              if target < candidates[i]:return 
              self.dfs(candidates,target-candidates[i],i,reslist+[candidates[i]])
          
          
      # DFS, not sort array (220ms)
      def combinationSum(self, candidates, target):
          self.result = []
          self.dfs(candidates,0,target,[])
          return self.result
          
      def dfs(self,can,cursum,target,res):
          if cursum > target: return 
          if cursum == target: 
              self.result.append(res)
              return 
          for i in xrange(len(can)):
              if not res or res[len(res)-1] <= can[i]:
                  self.dfs(can,cursum+can[i],target,res+[can[i]])
  
subject: Create combination_sum.py