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:

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#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);
}

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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:

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

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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"?

;)
i just meant
1 2

;)
1 has 2 as one of its element ...right??...i meant that

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.

Quote:

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Originally Posted by tabstop

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

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

Code:

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

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Quote:

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Originally Posted by linuxdude

I think clear() would be more convenient for removing everything.

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I agree, and if one wants to actually reduce capacity in addition to just reducing size, the swap trick should be used, e.g.,

Code:

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std::vector<long long int>().swap(g[0]);

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By the way, dpp, mind not using long long int in your examples when it is not necessary? It is not yet part of standard C++.

I did not know updation was a word.
http://www.google.com/search?source=...earch&aq=f&oq=