[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 · 2.5k 阅读

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本文详细介绍了使用深度优先搜索(DFS)实现组合求和问题的两种方法。通过递归调用，结合候选数的排序，有效地找出所有可能的组合，使得这些组合中数的总和等于目标值。文章提供了完整的C++代码示例，并通过具体实现展示了如何避免重复解。

class Solution {
//DFS
//sort candidates first and then DFS
public:
	vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
		// Start typing your C/C++ solution below
		// DO NOT write int main() function
		sort(candidates.begin(), candidates.end());
		vector<vector<int>> ans;
		vector<int> path;
		combinationSum_aux(0, 0, target, path, ans, candidates);
		return ans;
	}

	void combinationSum_aux( int index, int sumNow, int target, vector<int> path, vector<vector<int>>& ans, vector<int>& candidates ) 
	{
		//throw std::exception("The method or operation is not implemented.");
		if(sumNow == target)
		{
			ans.push_back(path);
			return;
		}
		if(index >= candidates.size())
			return;
		int num = (target-sumNow)/candidates[index];
		int cur = 0;
		for (int i = 0; i <= num; ++i)
		{
			combinationSum_aux(index+1, sumNow+cur, target, path, ans, candidates);
			path.push_back(candidates[index]);
			cur += candidates[index];
		}

	}


};

second time

class Solution {
public:
    void combinationSumUtil(vector<int>& candidates, int target, int curIdx, vector<int> curPath, vector<vector<int> >& allPath)
    {
        if(target == 0)
        {
            allPath.push_back(curPath);
            return ;
        }
        if(curIdx >= candidates.size()) return;        
        
        if(curIdx >= 1 && candidates[curIdx] == candidates[curIdx-1]) combinationSumUtil(candidates, target, curIdx+1, curPath, allPath);
        else
        {
            int curSum = 0;
            do
            {
                if(target >= curSum) combinationSumUtil(candidates, target-curSum, curIdx+1, curPath, allPath);
                curPath.push_back(candidates[curIdx]);
                curSum += candidates[curIdx];
            }
            while(target >= curSum);
            
        }
    }
    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        sort(candidates.begin(), candidates.end());
        vector<int> curPath;
        vector<vector<int> > allPath;
        combinationSumUtil(candidates, target, 0, curPath, allPath);
        return allPath;
    }
};