The answer is incorrect

#1

Predict the time complexity of the following recursive function, given the vector is of size N and the initial call is calSum(v, 0).

int sum = 0;
void calcSum(vector v, int i)
{
if(i == v.size())
return;
sum += v[i];
calcSum(v, i+1);
}

//The answer should be O( N )

#3

@harshit_2234
its correct ans should be o(n*n) here explanation
So you have the given function as :-

int sum=0;`

void calcSum(vector<int> v,int i){  // call by value
    if(i==v.size()){
        return ;
    }
    sum+=v[i];
    calcSum(v,i+1);
    return ;
}

you will notice that here function here is called by value
so every time you call the function then our original vector will be copied by the function and u know that copying a vector take O(n) so calling our function n times with subsequent copies will give us over all time complexity as O(n^2)
have the given function been like

int sum=0;

void calcSum(vector<int> &v,int i){ // call by reference 
    if(i==v.size()){
        return ;
    }
    sum+=v[i];
    calcSum(v,i+1);
    return ;
}

the time complexity would have been O(n)
dont forget to hit like and mark resolved if cleared :smiley:

1 Like