[LeetCode]Permutations II

最新推荐文章于 2019-05-11 19:52:40 发布

原创最新推荐文章于 2019-05-11 19:52:40 发布 · 2.5k 阅读

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本文介绍了一种使用C++实现的去除重复排列的算法。通过排序和标记已使用元素的方法，确保了在生成全排列时不产生重复项。适用于解决LeetCode等平台上的排列问题。

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class Solution {
//DFS
//always let the next same element go first, 
//in such a case we can cut down half same permutations 
//generated by these same element
//need more practice
public:
	vector<vector<int> > permuteUnique(vector<int> &num) {
		// Start typing your C/C++ solution below
		// DO NOT write int main() function
		int n = num.size();
		if(0 == n) return vector<vector<int> >();
		sort(num.begin(), num.end());
		vector<bool> used(num.size(), false);
		vector<vector<int>> ans;

		vector<int> path;
		permute_aux(n, used, path, ans, num);
		return ans;
	}

	void permute_aux( int n, vector<bool>& used, vector<int>& path, vector<vector<int>>& ans, const vector<int>& num ) 
	{
		//throw std::exception("The method or operation is not implemented.");
		if(0 == n) 
		{
			ans.push_back(path);
			return;
		}
		for (int i = 0; i < used.size(); ++i)
		{
			if(true == used[i] || (i != 0 && num[i] == num[i-1] && used[i-1]))
				continue;
			used[i] = true;
			path.push_back(num[i]);
			permute_aux(n-1, used, path, ans, num);
			used[i] = false;
			path.pop_back();
		}
	}
};

second time

class Solution {
public:
    void permuteUtil(vector<int>& num, vector<bool>& used, vector<int>& path, vector<vector<int> >& allPath)
    {
        if(path.size() == num.size())
        {
            allPath.push_back(path);
            return ;
        }
        for(int i = 0; i < num.size(); ++i)
        {
            if(i >= 1 && num[i] == num[i-1] && used[i-1] == false) continue;
            if(!used[i])
            {
                used[i] = true;
                path.push_back(num[i]);
                permuteUtil(num, used, path, allPath);
                path.pop_back();
                used[i] = false;
            }
        }
    }
    vector<vector<int> > permuteUnique(vector<int> &num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        sort(num.begin(), num.end());
        vector<vector<int> > allPath;
        vector<int> path;
        vector<bool> used(num.size(), false);
        permuteUtil(num, used, path, allPath);
        return allPath;
    }
};