【剑指offer】题52：构建乘积数组

注意反序遍历数组时

auto i = vec.size()-1;

i 为无符号整形

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vector<int> multiply(const vector<int>& A){    vector<int> re(A.size());    if (A.size()<=1)    {        return re;    }    vector<int> C(A.size(),1);    vector<int> D(A.size(),1);    for (auto i = 1; i < A.size();++i)    {        C[i] = C[i - 1] * A[i - 1];    }    for (int i = A.size()-2; i >= 0;--i)//auto -> unsigned int    {        D[i] = D[i + 1] * A[i + 1];    }    for (auto i = 0; i < A.size();++i)    {        re[i] = C[i] * D[i];    }    return re;}

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