Old Legos

input/code.cpp: In function 'int main()':
input/code.cpp:68:18: warning: suggest parentheses around comparison in operand of '&' [-Wparentheses]
   68 |     if (turn & 2 == 0) {
      |                ~~^~~~

#define F first
#define S second
#define PB push_back
#define MP make_pair
#define REP(i, a, b) for (int i = a; i < b; ++i)
#define BR "\n"

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<bool> vb;
typedef pair<int, int> pi;

void dfs(int s, vi adj[], bool vis[]) {
  if (vis[s]) {
    return;
  }
  vis[s] = true;
  // process s
  for (auto u : adj[s]) {
    dfs(u, adj, vis);
  }
}

bool comp(pi a, pi b) { return a.F - a.S < b.F - b.S; }
int value(pi a) { return a.F - a.S; }

int main() {
  // uncomment if io is a bottleneck
  // ios::sync_with_stdio(0);
  // cin.tie(0);

  // uncomment to read cin from a file
  // freopen("c.txt", "r", stdin);

  int n;
  cin >> n;

  vector<pi> lego;
  vector<int> left;
  vector<pair<pi, int>> byUo;
  vector<pair<pi, int>> byMaija;

  REP(i, 0, n) {
    int a, b;
    cin >> a >> b;
    lego.PB(MP(a, b));
    byUo.PB(MP(MP(a, b), i));
    byMaija.PB(MP(MP(b, a), i));
  }

  auto lego2 = lego;
  sort(lego.rbegin(), lego.rend(), comp);
  sort(lego2.begin(), lego2.end(), comp);
  // sort(byUo.rbegin(), byUo.rend());
  // sort(byMaija.rbegin(), byMaija.rend());

  int res = 0;
  int turn = 0;

  int i, j;
  i = 0;
  j = n - 1;
  while (i != j) {
    if (turn & 2 == 0) {
      res += value(lego[i]);
    } else {
      res -= value(lego[j]);
    }
    ++i;
    --j;
    turn++;
  }

  cout << res << BR;

  return EXIT_SUCCESS;
}

Test 1

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Test 2

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Test 3

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Test 4

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Test 65

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Test 66

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Test 68

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Test 69

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