leetcode: 40. Combination Sum II

# coding=utf-8

# Given a collection of candidate numbers (C) and a target number (T),
# find all unique combinations in C where the candidate numbers sums to T.
# 
# Each number in C may only be used once in the combination.
# 
# 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 10,1,2,7,6,1,5 and target 8, 
# A solution set is: 
# [1, 7] 
# [1, 2, 5] 
# [2, 6] 
# [1, 1, 6]

# DFS
class Solution():
    def combinationSum2(self, x, target):
        x.sort()
        res = []
        self.dfs(res, x, target-0, 0, [])
        return res
    def dfs(self, res, x, diff, start, path):
        if diff == 0 and path not in res:   # 加上 path not in res 来去重
            res.append(path)
        elif diff > 0:
            for j in range(start, len(x)):
                # 改为 self.dfs(res, x, diff-x[j], j, path+[x[j]]) 则 子数组 内 可含有 下标相同的元素
                self.dfs(res, x, diff-x[j], j+1, path+[x[j]])



if __name__ == "__main__":
    assert Solution().combinationSum2([10, 1, 2, 7, 6, 1, 5], 8) == [[1, 1, 6], [1, 2, 5], [1, 7], [2, 6]]