Problem p00930 (C++)

Buggy submission (status: Runtime Error):
#include <iostream>
#include <set>
#include <string>
#include <vector>
#define inf 1000000000

using namespace std;

struct SegTree {
  int size;
  vector<int> seg, delay;

  SegTree() {}
  SegTree(int size) {
    this->size = size;
    seg.resize(1 << (size + 1));
    delay.resize(1 << (size + 1));
  }

  void init() {
    for (int i = 0; i < (1 << (size + 1)); i++) {
      seg[i] = inf;
      delay[i] = 0;
    }
  }

  void eval(int l, int r, int k) {
    if (delay[k]) {
      seg[k] += delay[k];
      delay[k * 2] += delay[k];
      delay[k * 2 + 1] += delay[k];
      delay[k] = 0;
    }
  }

  void update(int i, int val) {
    i += (1 << size);
    seg[i] = val;
    while (i > 1) {
      i /= 2;
      seg[i] = min(seg[i * 2], seg[i * 2 + 1]);
    }
  }

  void add(int a, int b, int k, int l, int r, int val) {
    eval(l, r, k);

    if (b < l || r < a)
      return;
    if (a <= l && r <= b) {
      delay[k] += val;
      eval(l, r, k);
      return;
    }
    add(a, b, k * 2, l, (l + r) / 2, val);
    add(a, b, k * 2 + 1, (l + r) / 2 + 1, r, val);
    seg[k] = min(seg[k * 2], seg[k * 2 + 1]);
  }
  void add(int a, int b, int val) {
    if (a > b)
      return;
    add(a, b, 1, 0, (1 << size) - 1, val);
  }

  int query(int a, int b, int k, int l, int r) {
    eval(l, r, k);

    if (b < l || r < a)
      return inf;
    if (a <= l && r <= b)
      return seg[k];
    int lval = query(a, b, k * 2, l, (l + r) / 2);
    int rval = query(a, b, k * 2 + 1, (l + r) / 2 + 1, r);
    return min(lval, rval);
  }
  int query(int a, int b) { return query(a, b, 1, 0, (1 << size) - 1); }
};

int N, Q;
string s;
SegTree seg(19);
set<int> cand;

int getans(int p) {
  int ub = p, lb = 0, mid;
  while (ub - lb > 1) {
    mid = (ub + lb) / 2;
    if (seg.query(mid, p) >= 2)
      ub = mid;
    else
      lb = mid;
  }
  return ub;
}

int main(void) {
  cin >> N >> Q;
  cin >> s;
  s = " " + s;

  seg.init();
  int sum = 0;
  for (int i = 1; i <= N; i++) {
    if (s[i] == '(')
      sum++;
    else {
      sum--;
      cand.insert(i);
    }
    seg.update(i, sum);
  }

  int p, ans;
  for (int q = 0; q < Q; q++) {
    cin >> p;
    if (s[p] == '(') {
      s[p] = ')';
      cand.insert(p);
      seg.add(p, N, -2);

      while (s[*cand.begin()] == '(')
        cand.erase(cand.begin());
      ans = *cand.begin();
      s[ans] = '(';
      cand.erase(cand.begin());
      seg.add(ans, N, 2);
    } else {
      s[p] = '(';
      if (cand.count(p))
        cand.erase(p);
      seg.add(p, N, 2);

      ans = getans(p);
      s[ans] = ')';
      cand.insert(ans);
      seg.add(ans, N, -2);
    }
    cout << ans << endl;
  }

  return 0;
}


Fixed submission:
#include <iostream>
#include <set>
#include <string>
#include <vector>
#define inf 1000000000

using namespace std;

struct SegTree {
  int size;
  vector<int> seg, delay;

  SegTree() {}
  SegTree(int size) {
    this->size = size;
    seg.resize(1 << (size + 1));
    delay.resize(1 << (size + 1));
  }

  void init() {
    for (int i = 0; i < (1 << (size + 1)); i++) {
      seg[i] = inf;
      delay[i] = 0;
    }
  }

  void eval(int l, int r, int k) {
    if (delay[k]) {
      seg[k] += delay[k];
      if (l < r) {
        delay[k * 2] += delay[k];
        delay[k * 2 + 1] += delay[k];
      }
      delay[k] = 0;
    }
  }

  void update(int i, int val) {
    i += (1 << size);
    seg[i] = val;
    while (i > 1) {
      i /= 2;
      seg[i] = min(seg[i * 2], seg[i * 2 + 1]);
    }
  }

  void add(int a, int b, int k, int l, int r, int val) {
    eval(l, r, k);

    if (b < l || r < a)
      return;
    if (a <= l && r <= b) {
      delay[k] += val;
      eval(l, r, k);
      return;
    }
    add(a, b, k * 2, l, (l + r) / 2, val);
    add(a, b, k * 2 + 1, (l + r) / 2 + 1, r, val);
    seg[k] = min(seg[k * 2], seg[k * 2 + 1]);
  }
  void add(int a, int b, int val) {
    if (a > b)
      return;
    add(a, b, 1, 0, (1 << size) - 1, val);
  }

  int query(int a, int b, int k, int l, int r) {
    eval(l, r, k);

    if (b < l || r < a)
      return inf;
    if (a <= l && r <= b)
      return seg[k];
    int lval = query(a, b, k * 2, l, (l + r) / 2);
    int rval = query(a, b, k * 2 + 1, (l + r) / 2 + 1, r);
    return min(lval, rval);
  }
  int query(int a, int b) { return query(a, b, 1, 0, (1 << size) - 1); }
};

int N, Q;
string s;
SegTree seg(19);
set<int> cand;

int getans(int p) {
  int ub = p, lb = 0, mid;
  while (ub - lb > 1) {
    mid = (ub + lb) / 2;
    if (seg.query(mid, p) >= 2)
      ub = mid;
    else
      lb = mid;
  }
  return ub;
}

int main(void) {
  cin >> N >> Q;
  cin >> s;
  s = " " + s;

  seg.init();
  int sum = 0;
  for (int i = 1; i <= N; i++) {
    if (s[i] == '(')
      sum++;
    else {
      sum--;
      cand.insert(i);
    }
    seg.update(i, sum);
  }

  int p, ans;
  for (int q = 0; q < Q; q++) {
    cin >> p;
    if (s[p] == '(') {
      s[p] = ')';
      cand.insert(p);
      seg.add(p, N, -2);

      while (s[*cand.begin()] == '(')
        cand.erase(cand.begin());
      ans = *cand.begin();
      s[ans] = '(';
      cand.erase(cand.begin());
      seg.add(ans, N, 2);
    } else {
      s[p] = '(';
      if (cand.count(p))
        cand.erase(p);
      seg.add(p, N, 2);

      ans = getans(p);
      s[ans] = ')';
      cand.insert(ans);
      seg.add(ans, N, -2);
    }
    cout << ans << endl;
  }

  return 0;
}