LeetCode 39. Combination Sum

Given a set of candidate numbers (C) (without duplicates) 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]
]

完全背包输出所有路径问题

可以用完全背包求一遍，用vector<int>来维护所有到达该点的前驱结点。

然后从目标位置，开始往前搜索。注意剪枝一下， 可以去除重复路径。

class Solution
{
    void dfs(vector<vector<int>> &vec, int target, int pro, vector<vector<int>> &ans, vector<int> res)
    {
        for(auto &f : vec[target])
        {
            if(target - f > pro)
                return ;
            res.push_back(target - f);

            if(f != 0)
                dfs(vec, f, target-f, ans, res);
            else
                ans.push_back(res);
            res.pop_back();
        }
    }

public:
    vector<vector<int>> combinationSum(vector<int>& candidates, int target)
    {
        sort(candidates.begin(), candidates.end());

        vector<bool> dp(target+1, false);
        dp[0] = true;

        vector<vector<int>>vec(target+1);

        for(int i = 0; i < candidates.size(); ++ i)
        {
            for(int j = candidates[i]; j <= target; ++ j)
            {
                if(dp[j-candidates[i]])
                {
                    dp[j] = true;
                    vec[j].push_back(j-candidates[i]);
                }
            }
        }
        vector<vector<int>>ans;

        dfs(vec, target, target, ans, vector<int> {});

        return ans;
    }
};