Problem p02599 (C++) — buggy submission, verdict: Runtime Error

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

template <class Abel> struct BIT {
  vector<Abel> dat[2];
  Abel UNITY_SUM = 0; // to be set

  /* [1, n] */
  BIT(int n) { init(n); }
  void init(int n) {
    for (int iter = 0; iter < 2; ++iter)
      dat[iter].assign(n + 1, UNITY_SUM);
  }

  /* a, b are 1-indexed, [a, b) */
  inline void sub_add(int p, int a, Abel x) {
    for (int i = a; i < (int)dat[p].size(); i += i & -i)
      dat[p][i] = dat[p][i] + x;
  }
  inline void add(int a, int b, Abel x) {
    sub_add(0, a, x * -(a - 1));
    sub_add(1, a, x);
    sub_add(0, b, x * (b - 1));
    sub_add(1, b, x * (-1));
  }

  /* a is 1-indexed, [a, b) */
  inline Abel sub_sum(int p, int a) {
    Abel res = UNITY_SUM;
    for (int i = a; i > 0; i -= i & -i)
      res = res + dat[p][i];
    return res;
  }
  inline Abel sum(int a, int b) {
    return sub_sum(0, b - 1) + sub_sum(1, b - 1) * (b - 1) - sub_sum(0, a - 1) -
           sub_sum(1, a - 1) * (a - 1);
  }

  /* debug */
  void print() {
    for (int i = 1; i < (int)dat[0].size(); ++i)
      cout << sum(i, i + 1) << ",";
    cout << endl;
  }
};

int main() {
  int N;
  int Q;
  cin >> N >> Q;
  vector<int> a(N);
  for (int i = 0; i < N; ++i)
    cin >> a[i];

  vector<int> lefts(Q), rights(Q), ids(Q);
  for (int i = 0; i < Q; ++i) {
    cin >> lefts[i] >> rights[i];
    --lefts[i];
    ids[i] = i;
  }
  sort(ids.begin(), ids.end(),
       [&](int i, int j) { return rights[i] < rights[j]; });

  BIT<int> bit(N + 5);
  vector<int> prev(1100000, -1);
  vector<int> res(Q, 0);
  int r = 0;
  for (auto i : ids) {
    for (; r < rights[i]; ++r) {
      bit.add(prev[a[r]] + 2, r + 2, 1);
      prev[a[r]] = r;
    }
    int tmp = bit.sum(lefts[i] + 1, lefts[i] + 2);
    res[i] = max(res[i], tmp);
  }
  for (int i = 0; i < Q; ++i)
    cout << res[i] << endl;
}

Error: 0

Fixed submission:

#include <stdio.h>
// C++ implementation of above approach
#include <bits/stdc++.h>
using namespace std;

// Each segment of the segment tree would be a set
// to maintain distinct elements
set<int> *segment;

// Build the segment tree
// i denotes current node, s denotes start and
// e denotes the end of range for current node
void build(int i, int s, int e, std::vector<int> &arr) {

  // If start is equal to end then
  // insert the array element
  if (s == e) {
    segment[i].insert(arr[s]);
    return;
  }

  // Else divide the range into two halves
  // (start to mid) and (mid+1 to end)
  // first half will be the left node
  // and the second half will be the right node
  build(2 * i, s, (s + e) / 2, arr);
  build(1 + 2 * i, 1 + (s + e) / 2, e, arr);

  // Insert the sets of right and left
  // node of the segment tree
  segment[i].insert(segment[2 * i].begin(), segment[2 * i].end());

  segment[i].insert(segment[2 * i + 1].begin(), segment[2 * i + 1].end());
}

// Query in an range a to b
set<int> query(int node, int l, int r, int a, int b) {
  set<int> left, right, result;

  // If the range is out of the bounds
  // of this segment
  if (b < l || a > r)
    return result;

  // If the range lies in this segment
  if (a <= l && r <= b)
    return segment[node];

  // Else query for the right and left
  // leaf node of this subtree
  // and insert them into the set
  left = query(2 * node, l, (l + r) / 2, a, b);
  result.insert(left.begin(), left.end());

  right = query(1 + 2 * node, 1 + (l + r) / 2, r, a, b);
  result.insert(right.begin(), right.end());

  // Return the result
  return result;
}

// Initialize the segment tree
void init(int n) {
  // Get the height of the segment tree
  int h = (int)ceil(log2(n));
  h = (2 * (pow(2, h))) - 1;

  // Initialize the segment tree
  segment = new set<int>[h];
}

// Function to get the result for the
// subarray from arr[l] to arr[r]
void getDistinct(int l, int r, int n) {
  // Query for the range set
  set<int> ans = query(1, 0, n - 1, l, r);

  cout << ans.size() << endl;
}

// Driver code
int main() {

  int n;
  int q;
  std::cin >> n >> q;

  std::vector<int> c;
  for (int i = 0; i < n; i++) {
    int a;
    std::cin >> a;
    c.push_back(a);
  }

  std::vector<std::pair<int, int>> queries;
  for (int i = 0; i < q; i++) {
    int a;
    int b;
    std::cin >> a >> b;
    queries.push_back(std::make_pair(a - 1, b - 1));
  }

  init(n);

  // Bulid the segment tree
  build(1, 0, n - 1, c);

  // Query in range 0 to 4
  for (const auto &elem : queries) {
    getDistinct(elem.first, elem.second, n);
  }

  return 0;
}