LeetCode #39. Combination Sum

Problem Statement

(Source) 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.

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]
]

Solution

class Solution(object):

def bt(self, candidates, target, start_index, n, ass, res):
if target == 0:
res.add(tuple(ass))
else:
for index in xrange(start_index, n):
if candidates[index] > target:
break
ass.append(candidates[index])
self.bt(candidates, target - candidates[index], index, n, ass, res)
ass.pop()

def combinationSum(self, candidates, target):
"""
:type candidates: List[int]
:type target: int
:rtype: List[List[int]]
"""
candidates.sort()
res = set()
self.bt(candidates, target, 0, len(candidates), [], res)
return [list(tup) for tup in res]