Preview:
#include<bits/stdc++.h>
using namespace std;
int sum=0;
vector<int> rev(vector<int>& nums,int f,int r)
{
    if(f<=r)
    {
        swap(nums[f],nums[r]);
        rev(nums,f+1,r-1);
    }
    return nums;
}
int main()
{

    vector<int> v = {4,5,2,6,3,56,5};
    rev(v,0,6);
    for(int i=0;i<=6;++i)
    cout<<v[i]<<" ";
    
}
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