combination-sum

最新推荐文章于 2019-11-28 19:45:51 发布

llwjason5555

最新推荐文章于 2019-11-28 19:45:51 发布

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分类专栏： leetcode 文章标签： leetcode 递归

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本文针对给定候选数集合及目标数，寻找所有可能的组合，使得候选数之和等于目标数。通过递归方法实现，确保组合唯一且非降序排列。

题目：

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 (a 1, a 2, … , a k) must be in non-descending order. (ie, a 1 ≤ a 2 ≤ … ≤ a k).
The solution set must not contain duplicate combinations.

For example, given candidate set2,3,6,7and target7,
A solution set is:
[7]
[2, 2, 3]

程序：

class Solution {
public:
    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        set<vector<int>> s;
        sum(candidates, target, s);
        vector<vector<int>> res(s.begin(), s.end());
        return res;
    }

    void sum(vector<int> &candidates, int target, set<vector<int>> &res)
    {
        vector<int> temp;
        if (target == 0)
        {
            temp = v;
            sort(temp.begin(), temp.end());//若此处直接使用v来排序，会改变v的顺序，pop_back时会出现错误
            res.insert(temp);
            return;
        }
        else if (target < 0)
            return;

        for (int i = 0; i < candidates.size(); i++)
        {
            v.push_back(candidates[i]);
            sum(candidates, target - candidates[i], res);
            v.pop_back();

        }

    }
    vector<int> v;
};