How can I fill a map of int and vector<int> in C++?

Question

I have been working with <map>, where I declared a map as follows:

map <int, vector<int> > tree;

I am now trying to assign values to it. My goal is to place multiple values as elements of its keys. Something like this:

0=null
1=>0
2=>1,0
3=>2,1,0
4=>3,2,1,0
5=>0

I tried to assign to the map like this, but it does not work:

tree[3]=vector<int>(2,1,0);

However, the following two ways of assigning work:

tree[1]=vector<int>(0);
tree[2]=vector<int>(1,0);

Where is the problem? How can I make a function that works as a Python dictionary?

I am not using C++11.

Answer 1

With C++11, you could try:

tree[3]=vector<int>({2,1,0});

^{Other than that, the question could use more details and some code of what you already tried...}