Problem p03519 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define REP(i, n) for (LL i = 0; i < (LL)(n); i++)
#define ALL(x) (x).begin(), (x).end()
#define LL long long
#define pii pair<LL, LL>
#define pll pair<LL, LL>

using namespace std;

struct SegmentTree {

  LL n;
  vector<LL> data;
  vector<LL> num;
  vector<LL> minusmax;
  vector<LL> plusmin;

  SegmentTree(LL _n) {
    n = 2;
    while (n < _n)
      n *= 2;
    data.resize(2 * n - 1, INT_MIN);
    num.resize(2 * n - 1, 0);
    minusmax.resize(2 * n - 1, INT_MIN);
    plusmin.resize(2 * n - 1, INT_MAX);
  }

  void set(LL pos, LL x) {
    pos += n - 1;
    data[pos] = x;
    if (x > 0) {
      num[pos] = 1;
      plusmin[pos] = x;
      minusmax[pos] = INT_MIN;
    } else {
      num[pos] = 0;
      minusmax[pos] = x;
      plusmin[pos] = INT_MAX;
    }
    while (pos > 0) {
      pos = (pos - 1) / 2;
      data[pos] = (max(0LL, data[2 * pos + 1]) + max(0LL, data[2 * pos + 2]));
      num[pos] = num[2 * pos + 1] + num[2 * pos + 2];
      minusmax[pos] = max(minusmax[2 * pos + 1], minusmax[2 * pos + 2]);
      plusmin[pos] = min(plusmin[2 * pos + 1], plusmin[2 * pos + 2]);
    }
  }

  LL getSum(LL l, LL r, LL a = 0, LL b = -1, LL pos = 0) {
    if (b < 0)
      b = n;
    if (l >= b || r <= a)
      return 0;
    if (l <= a && r <= b)
      return max(0LL, data[pos]);
    return getSum(l, r, a, (a + b) / 2, pos * 2 + 1) +
           getSum(l, r, (a + b) / 2, b, pos * 2 + 2);
  }
  LL getNum(LL l, LL r, LL a = 0, LL b = -1, LL pos = 0) {
    if (b < 0)
      b = n;
    if (l >= b || r <= a)
      return 0;
    if (l <= a && r <= b)
      return num[pos];
    return getNum(l, r, a, (a + b) / 2, pos * 2 + 1) +
           getNum(l, r, (a + b) / 2, b, pos * 2 + 2);
  }
  LL getMinusMax(LL l, LL r, LL a = 0, LL b = -1, LL pos = 0) {
    if (b < 0)
      b = n;
    if (l >= b || r <= a)
      return INT_MIN;
    if (l <= a && r <= b)
      return minusmax[pos];
    return max(getMinusMax(l, r, a, (a + b) / 2, pos * 2 + 1),
               getMinusMax(l, r, (a + b) / 2, b, pos * 2 + 2));
  }
  LL getPlusMin(LL l, LL r, LL a = 0, LL b = -1, LL pos = 0) {
    if (b < 0)
      b = n;
    if (l >= b || r <= a)
      return INT_MAX;
    if (l <= a && r <= b)
      return plusmin[pos];
    return min(getPlusMin(l, r, a, (a + b) / 2, pos * 2 + 1),
               getPlusMin(l, r, (a + b) / 2, b, pos * 2 + 2));
  }

  void printData() {
    cout << endl;
    REP(i, n) cout << n - 1 + i << " " << data[n - 1 + i] << endl;
    cout << endl;
  }
};

int main() {

  LL N, Q;
  cin >> N >> Q;
  LL ans = 0;
  LL a[2 * N], b[2 * N];

  REP(i, 2 * N) cin >> a[i];
  REP(i, 2 * N) cin >> b[i];

  if (N == 1) {
    while (Q--) {
      LL p, x, y;
      cin >> p >> x >> y;
      a[--p] = x;
      ans = a[0] + a[1];
      cout << ans << endl;
    }
  } else {
    REP(i, 2 * N) ans += a[i];
    SegmentTree st(2 * N - 2);
    REP(i, 2 * N - 2) st.set(i, b[i + 1] - a[i + 1]);

    while (Q--) {
      LL p, x, y;
      cin >> p >> x >> y;
      ans -= a[--p];
      a[p] = x;
      b[p] = y;
      ans += a[p];
      st.set(p - 1, y - x);

      LL res = ans + st.getSum(0, 2 * N - 2);
      if (st.getNum(0, 2 * N - 2) % 2 == 1) {
        res = max(res - st.getPlusMin(0, 2 * N - 2),
                  res + st.getMinusMax(0, 2 * N - 2));
      }

      cout << res << endl;
    }
  }
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
#define REP(i, n) for (LL i = 0; i < (LL)(n); i++)
#define ALL(x) (x).begin(), (x).end()
#define LL long long
#define pii pair<LL, LL>
#define pll pair<LL, LL>

using namespace std;

struct SegmentTree {

  LL n;
  vector<LL> data;
  vector<LL> num;
  vector<LL> minusmax;
  vector<LL> plusmin;

  SegmentTree(LL _n) {
    n = 2;
    while (n < _n)
      n *= 2;
    data.resize(2 * n - 1, INT_MIN);
    num.resize(2 * n - 1, 0);
    minusmax.resize(2 * n - 1, INT_MIN);
    plusmin.resize(2 * n - 1, INT_MAX);
  }

  void set(LL pos, LL x) {
    pos += n - 1;
    data[pos] = x;
    if (x > 0) {
      num[pos] = 1;
      plusmin[pos] = x;
      minusmax[pos] = INT_MIN;
    } else {
      num[pos] = 0;
      minusmax[pos] = x;
      plusmin[pos] = INT_MAX;
    }
    while (pos > 0) {
      pos = (pos - 1) / 2;
      data[pos] = (max(0LL, data[2 * pos + 1]) + max(0LL, data[2 * pos + 2]));
      num[pos] = num[2 * pos + 1] + num[2 * pos + 2];
      minusmax[pos] = max(minusmax[2 * pos + 1], minusmax[2 * pos + 2]);
      plusmin[pos] = min(plusmin[2 * pos + 1], plusmin[2 * pos + 2]);
    }
  }

  LL getSum(LL l, LL r, LL a = 0, LL b = -1, LL pos = 0) {
    if (b < 0)
      b = n;
    if (l >= b || r <= a)
      return 0;
    if (l <= a && r <= b)
      return max(0LL, data[pos]);
    return getSum(l, r, a, (a + b) / 2, pos * 2 + 1) +
           getSum(l, r, (a + b) / 2, b, pos * 2 + 2);
  }
  LL getNum(LL l, LL r, LL a = 0, LL b = -1, LL pos = 0) {
    if (b < 0)
      b = n;
    if (l >= b || r <= a)
      return 0;
    if (l <= a && r <= b)
      return num[pos];
    return getNum(l, r, a, (a + b) / 2, pos * 2 + 1) +
           getNum(l, r, (a + b) / 2, b, pos * 2 + 2);
  }
  LL getMinusMax(LL l, LL r, LL a = 0, LL b = -1, LL pos = 0) {
    if (b < 0)
      b = n;
    if (l >= b || r <= a)
      return INT_MIN;
    if (l <= a && r <= b)
      return minusmax[pos];
    return max(getMinusMax(l, r, a, (a + b) / 2, pos * 2 + 1),
               getMinusMax(l, r, (a + b) / 2, b, pos * 2 + 2));
  }
  LL getPlusMin(LL l, LL r, LL a = 0, LL b = -1, LL pos = 0) {
    if (b < 0)
      b = n;
    if (l >= b || r <= a)
      return INT_MAX;
    if (l <= a && r <= b)
      return plusmin[pos];
    return min(getPlusMin(l, r, a, (a + b) / 2, pos * 2 + 1),
               getPlusMin(l, r, (a + b) / 2, b, pos * 2 + 2));
  }

  void printData() {
    cout << endl;
    REP(i, n) cout << n - 1 + i << " " << data[n - 1 + i] << endl;
    cout << endl;
  }
};

int main() {

  LL N, Q;
  cin >> N >> Q;
  LL ans = 0;
  LL a[2 * N], b[2 * N];

  REP(i, 2 * N) cin >> a[i];
  REP(i, 2 * N) cin >> b[i];

  if (N == 1) {
    while (Q--) {
      LL p, x, y;
      cin >> p >> x >> y;
      a[--p] = x;
      ans = a[0] + a[1];
      cout << ans << endl;
    }
  } else {
    REP(i, 2 * N) ans += a[i];
    SegmentTree st(2 * N - 2);
    REP(i, 2 * N - 2) st.set(i, b[i + 1] - a[i + 1]);

    while (Q--) {
      LL p, x, y;
      cin >> p >> x >> y;
      ans -= a[--p];
      a[p] = x;
      b[p] = y;
      ans += a[p];
      if (p != 0 && p != 2 * N - 1)
        st.set(p - 1, y - x);

      LL res = ans + st.getSum(0, 2 * N - 2);
      if (st.getNum(0, 2 * N - 2) % 2 == 1) {
        res = max(res - st.getPlusMin(0, 2 * N - 2),
                  res + st.getMinusMax(0, 2 * N - 2));
      }

      cout << res << endl;
    }
  }
  return 0;
}