[Leetcode] Combination Sum

最新推荐文章于 2019-05-21 16:08:00 发布

原创最新推荐文章于 2019-05-21 16:08:00 发布 · 232 阅读

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本文介绍了一种通过深度优先搜索（DFS）算法解决给定候选数集与目标数求和问题的方法。算法首先对候选数进行排序，然后递归地在候选数集中查找所有可能的组合，确保找到的所有组合都是非降序排列且不包含重复元素。

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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 (a₁, a₂, â€¦ , a_k) must be in non-descending order. (ie, a₁ â‰¤ a₂ â‰¤ â€¦ â‰¤ a_k).
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]

DFS

class Solution {
public:
    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<vector<int> > result;
        vector<int> com;
        sort(candidates.begin(),candidates.end());
        
        dfs(result,com,candidates,0,target);
        return result;      
    }
    
    void dfs (vector<vector<int> > &result, vector<int> &com, vector<int> &candidate, int index, int target)
    {
        
       for(int i=index;i<candidate.size();i++)
        {
            if(candidate[index] == target)
            { 
                com.push_back(candidate[i]);
                result.push_back(com);
                com.pop_back();
                return;
            }
            else if(candidate[index] > target)
            {
                return;
            }
            else
            {
                com.push_back(candidate[i]);
                dfs(result,com,candidate,i,target-candidate[i]);
                com.pop_back();
            }
            index++;
        }
    }
};