Vector can be used to replace one-dimensional arrays. Vector provides the operator[] function, which can be operated like an array, and it also has bounds checking and dynamically changes its size.
It is only introduced here to replace the two-dimensional array, and so on.
1. Define a two-dimensional vector
vector<vector<int> > v;//注意>和>之间的空格。
2. Three ways to access elements of a two-dimensional vector
If you specify the size of the outer and inner vectors, you can use operator[] to read and write; if you only specify the size of the outer vector, you can use the push_back() function to write, but operator[] cannot be used to read and write.
1) Specify the size of the outer vector, which
can be initialized with the push_back function:
v.resize(3);
v[1].push_back(9);
2) Traverse the size of the specified inner vector Set the size of each line of vector in
advance , you can use operator[] to access, as follows:
for(int i=0;i<3;i++)
v[i].resize(3);
3) Specify the size of the inner and outer layer vectors at a time
v.resize(n, vector<int>(m));