c 2b 2b vector resize

1vector<vector<vector<double>>> f(3, vector<vector<double>>(4, vector<double>(5)));

1dp.resize(n+1,vector<vector<int>>(n+1,vector<int>(n+1,-1)));
2

1The C++ function std::vector::resize() changes the size of vector. If n is smaller than current size then extra elements are destroyed.
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3If n is greater than current container size then new elements are inserted at the end of vector.
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5If val is specified then new elements are initialed with val.

1std::vector<int> a = {1, 2};
2std::vector<int> b = {3, 4, 5};
3a.insert(a.end(), b.begin(), b.end()); // a = {1, 2, 3, 4, 5}

1std::vector<int> vec = {1, 2, 3};
2vec.resize(2); // {1, 2}
3vec.resize(4); // {1, 2, 0, 0,}
4vec.resize(6, 9);  // {1, 2, 0, 0, 9, 9}

1resize (size_type n, const value_type& val);
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3The resize() method (and passing argument to constructor is equivalent to that)
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5will insert or delete appropriate number of elements to the vector to make it
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7given size (it has optional second argument to specify their value).