[LeetCode] Backtracking Template for (Subsets, Permutations, and Combination Sum)

根据issac3 用Java总结了backtracking template, 我用他的方法改成了Python. 以下为template.

 def backtrack(ans, temp, nums, start): # 可能有start, 也可能没有
             if len(temp) == len(nums):
                 ans.append(temp)
             else:
                 for i in range(start, len(nums)):
                     if nums[i] not in temp:
                         backtrack(ans, temp + [nums[i]], nums, i + 1) # 如果可以重复利用同一个元素,那么 用 i

 ans = []
 nums.sort() # 可能需要sort
 backtrack(ans, [], nums, 0)
 return ans

可以用来解决的问题有: Leetcode 78. Subsets , Leetcode 90. Subsets II, Leetcode 46. Permutations, Leetcode 47. Permutations II(contains duplicates), Leetcode 39. Combination Sum, Leetcode 40. Combination Sum II, Leetcode 131. Palindrome Partitioning.