Problem p02599 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <map>
using namespace std;
const int MAXN = 5e5 + 5;
const int M = MAXN * 20;
int n, q, tot;
int a[MAXN];
int T[MAXN * 4], lson[M], rson[M], c[M];

int build(int l, int r) {
  int root = tot++;
  c[root] = 0;
  if (l != r) {
    int mid = (l + r) >> 1;
    lson[root] = build(l, mid);
    rson[root] = build(mid + 1, r);
  }
  return root;
}

int update(int root, int pos, int val) {
  int newroot = tot++, tmp = newroot;
  c[newroot] = c[root] + val;
  int l = 1, r = n;
  while (l < r) {
    int mid = (l + r) >> 1;
    if (pos <= mid) {
      lson[newroot] = tot++;
      rson[newroot] = rson[root];
      newroot = lson[newroot];
      root = lson[root];
      r = mid;
    } else {
      rson[newroot] = tot++;
      lson[newroot] = lson[root];
      newroot = rson[newroot];
      root = rson[root];
      l = mid + 1;
    }
    c[newroot] = c[root] + val;
  }
  return tmp;
}

int query(int root, int pos) {
  int ret = 0;
  int l = 1, r = n;
  while (pos < r) {
    int mid = (l + r) >> 1;
    if (pos <= mid) {
      r = mid;
      root = lson[root];
    } else {
      ret += c[lson[root]];
      root = rson[root];
      l = mid + 1;
    }
  }
  return ret + c[root];
}

int main() {
  cin >> n >> q;
  tot = 0;
  for (int i = 1; i <= n; i++)
    scanf("%d", &a[i]);
  T[n + 1] = build(1, n);
  map<int, int> mp;
  for (int i = n; i >= 1; i--) {
    if (mp.find(a[i]) == mp.end()) {
      T[i] = update(T[i + 1], i, 1);
    } else {
      int tmp = update(T[i + 1], mp[a[i]], -1);
      T[i] = update(tmp, i, 1);
    }
    mp[a[i]] = i;
  }
  while (q--) {
    int l, r;
    scanf("%d%d", &l, &r);
    printf("%d\n", query(T[l], r));
  }

  return 0;
}


Fixed submission:
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <map>
using namespace std;
const int MAXN = 5e5 + 5;
const int M = MAXN * 100;
int n, q, tot;
int a[MAXN];
int T[MAXN * 4], lson[M], rson[M], c[M];

int build(int l, int r) {
  int root = tot++;
  c[root] = 0;
  if (l != r) {
    int mid = (l + r) >> 1;
    lson[root] = build(l, mid);
    rson[root] = build(mid + 1, r);
  }
  return root;
}

int update(int root, int pos, int val) {
  int newroot = tot++, tmp = newroot;
  c[newroot] = c[root] + val;
  int l = 1, r = n;
  while (l < r) {
    int mid = (l + r) >> 1;
    if (pos <= mid) {
      lson[newroot] = tot++;
      rson[newroot] = rson[root];
      newroot = lson[newroot];
      root = lson[root];
      r = mid;
    } else {
      rson[newroot] = tot++;
      lson[newroot] = lson[root];
      newroot = rson[newroot];
      root = rson[root];
      l = mid + 1;
    }
    c[newroot] = c[root] + val;
  }
  return tmp;
}

int query(int root, int pos) {
  int ret = 0;
  int l = 1, r = n;
  while (pos < r) {
    int mid = (l + r) >> 1;
    if (pos <= mid) {
      r = mid;
      root = lson[root];
    } else {
      ret += c[lson[root]];
      root = rson[root];
      l = mid + 1;
    }
  }
  return ret + c[root];
}

int main() {
  cin >> n >> q;
  tot = 0;
  for (int i = 1; i <= n; i++)
    scanf("%d", &a[i]);
  T[n + 1] = build(1, n);
  map<int, int> mp;
  for (int i = n; i >= 1; i--) {
    if (mp.find(a[i]) == mp.end()) {
      T[i] = update(T[i + 1], i, 1);
    } else {
      int tmp = update(T[i + 1], mp[a[i]], -1);
      T[i] = update(tmp, i, 1);
    }
    mp[a[i]] = i;
  }
  while (q--) {
    int l, r;
    scanf("%d%d", &l, &r);
    printf("%d\n", query(T[l], r));
  }

  return 0;
}