Why the answer is given as O(n^2)?

#1

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

#2

@poorna883
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)

#3

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