Thread: Vector updation

Let me put up my requirement straight away

*I want The vector to be updated rather than creating a new vector

*Will the complexity (running time) be better?

say for eg:

Code:

#include<iostream>
#include<vector>
using namespace std;
int main()
{
    int i,j=0;
   
      vector < vector<long long int> > g(100);
g[1].push_back(2);
g[2].push_back(3);
         return(0);
}

now all i wanted to do is to update the vector after a few steps...
i want it to look like a new emplty vector with

Code:

2 associated with 1
3 associated with 2...ie just the reverse of the previous one...i want the previous associations to be removed

ofcourse i can do it by creating a new vector with the second associations alone....
but i dont need that...I want the original vector to be updated with minimal complexity

What do you mean by "associations"?

Okay. So you have 100 vectors. g[1] has one element which is 2. g[2] has one element which is 3. g[0], g[3], ..., g[99] are all empty. There's no previous state that I can see to get rid of.

If you wanted to clear g[1], you could use erase(), I guess.

ya u understood my question..

i just want hem to be updtaed with new associations say
now g[2] holds 1 (instead of g[1] holding 2)

If you want to remove everything from a vector, then you can use erase(). Alternatively, you can just overwrite entries; if g[2][0] is 3, and you want it to be 1, then just assign it with g[2][0] = 1.

Originally Posted by tabstop

If you want to remove everything from a vector, then you can use erase().

I think clear() would be more convenient for removing everything. However, you could you use

Code:

erase(vector.begin(), vector.end())