Leetcode解题-Combination Sum II

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描述

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]

分析

这次要求一个元素只能用一次（但同样数值的元素可能出现多次，我们用一个OrderedDict来存储计数），稍微修改Combination Sum中的答案就可以了。

代码

Python

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from collections import OrderedDict, Counter


class Solution(object):
    def dfs(self, candidates, target, path, rs):
        if target == 0:
            rs.append(path[:])
            return
        for c, v in candidates.iteritems():
            if v > 0 and (not path or c >= path[-1]) and target - c >= 0:
                path.append(c)
                candidates[c] -= 1
                self.dfs(candidates, target - c, path, rs)
                path.pop()
                candidates[c] += 1

    def combinationSum2(self, candidates, target):
        """
        :type candidates: List[int]
        :type target: int
        :rtype: List[List[int]]
        """
        if target <= 0:
            return []
        rs = []
        path = []
        c = Counter(candidates)
        candidates = OrderedDict(sorted(c.items()))
        self.dfs(candidates, target, path, rs)
        return rs

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