CodeForces 1749B (Death's Blessing)

[fallen slate]

I got the concept correct, but I keep getting runtime errors. I'm not very experienced with why different runtime errors happen. Does anyone know why I'm getting a runtime error?

[dreamy spire]

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[fallen slate]

!format

[dreamy spire]

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

// find the index where the largest value of b[i] is stored (largest spell)
// denoted as vi_max (vector-index max)
int max_vector_index(vector<int> const& v, int& vi_max) {
  for (int i = 0; i < v.size(); ++i) {
    vi_max = max(v[i], v[i + 1]);
  }
  return vi_max;
}

void solve() {
  int n, vi_max, h = 0;
  cin >> n;
  vector<int> a(n);
  vector<int> b(n);

  for (int i = 0; i < n; ++i) {
    cin >> a[i];
    h += a[i];
  }

  for (int i = 0; i < n; ++i) {
    cin >> b[i];
    h += b[i];
  }
  max_vector_index(b, vi_max);

  h -= b[vi_max];
  cout << h << '\n';
}

int main() {
  int t;
  cin >> t;
  while (t--) {
    solve();
  }
}

techy

[lunar jolt]

you should say what its' supposed to do, and also post the error you see

vi_max = max(v[i], v[i + 1]); this doesn't do what you want it to do

[warm robin]

Your max_vector_index reads memory out of bounds where i + 1 equals v.size() which would explain runtime errors.

also, I don't think it returns the index but rather the largest value which causes another OOB read in solve

you could use std::max_element to get the index for the max element like this

template <class FIt>
typename std::iterator_traits<FIt>::difference_type
max_element_index(
    FIt first, 
    FIt last
    ) 
{
    return std::distance(
               first, 
               std::max_element(first,
                                last));
}

[dreamy spire]

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