lurenaa的博客

😂失败1.超出时间

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class Solution {
public:
    int fourSumCount(vector<int>& A, vector<int>& B, vector<int>& C, vector<int>& D) {
        set<vector<int>> st;
        for(int a = 0; a < A.size(); ++a)
            for(int b = 0; b <B.size(); ++b)
                for(int c = 0; c < C.size(); ++c)
                    for(int d = 0; d < D.size(); ++d)
                    {
                        if(A[a] + B[b] + C[c] + D[d] == 0) {
                            st.insert({a,b,c,d});
                        }
                    }
        return st.size();
    }
};

😜分为两组

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class Solution {
public:
    int fourSumCount(vector<int>& A, vector<int>& B, vector<int>& C, vector<int>& D) {
        map<int,int> st;
        int count = 0;
        int x;
        for(int a = 0; a < A.size(); ++a)
            for(int b = 0; b <B.size(); ++b)
            {
                x = A[a] + B[b];
                if(!st.count(x))
                    st.insert({x, 1});
                else 
                    st[x] += 1;
            }

        for(int c = 0; c < C.size(); ++c)
            for(int d = 0; d < D.size(); ++d)
            {
                x = C[c] + D[d];
                if(st.count(-x)) {
                    count += st[-x];
                }
            }
        return count;
    }
};

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