Problem p04052 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>

using namespace std;

const int N = 4e5 + 10;

int n, k, a[N], pos[N], deg[N], ans[N];
vector<int> g[N];

#define LD (t << 1)
#define RD (t << 1 | 1)

int val[N << 2];

void build(int t, int l, int r) {
  val[t] = n + 1;
  if (l == r)
    return;
  int mid = (l + r) >> 1;
  build(LD, l, mid);
  build(RD, mid + 1, r);
}

void insert(int t, int l, int r, int pos, int vl) {
  val[t] = min(val[t], vl);
  if (l == r)
    return;
  int mid = (l + r) >> 1;
  if (pos <= mid)
    insert(LD, l, mid, pos, vl);
  else
    insert(RD, mid + 1, r, pos, vl);
}

int query(int t, int l, int r, int ql, int qr) {
  if (ql > qr)
    return n + 1;
  if (ql <= l && r <= qr)
    return val[t];
  int mid = (l + r) >> 1, res = n + 1;
  if (ql <= mid)
    res = min(res, query(LD, l, mid, ql, qr));
  if (qr > mid)
    res = min(res, query(RD, mid + 1, r, ql, qr));
  return res;
}

int main() {
  scanf("%d %d", &n, &k);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    pos[a[i]] = i;
  }
  build(1, 1, n);
  // for (int i = 1; i <= n; i++) {
  //   printf("%d ", pos[i]);
  // }
  // puts("");
  for (int i = n; i >= 1; i--) {
    int l = query(1, 1, n, max(1, pos[i] - k + 1), pos[i] - 1);
    int r = query(1, 1, n, pos[i] + 1, min(n, pos[i] + k - 1));
    // cout<<i<<" "<<l<<" "<<r<<endl;
    if (r <= n) {
      g[pos[i]].push_back(pos[r]);
      deg[pos[r]]++;
    }
    if (l <= n) {
      g[pos[i]].push_back(pos[l]);
      deg[pos[l]]++;
    }
    insert(1, 1, n, pos[i], i);
  }
  int cur = 0;
  priority_queue<int, vector<int>, greater<int>> q;
  for (int i = 1; i <= n; i++) {
    if (!deg[i]) {
      q.push(i);
    }
  }
  while (q.size()) {
    int u = q.top();
    q.pop();
    ans[u] = ++cur;
    for (auto v : g[u]) {
      if (!(--deg[v])) {
        q.push(v);
      }
    }
  }
  for (int i = 1; i <= n; i++) {
    printf("%d\n", ans[i]);
  }
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>

using namespace std;

const int N = 5e5 + 10;

int n, k, a[N], pos[N], deg[N], ans[N];
vector<int> g[N];

#define LD (t << 1)
#define RD (t << 1 | 1)

int val[N << 2];

void build(int t, int l, int r) {
  val[t] = n + 1;
  if (l == r)
    return;
  int mid = (l + r) >> 1;
  build(LD, l, mid);
  build(RD, mid + 1, r);
}

void insert(int t, int l, int r, int pos, int vl) {
  val[t] = min(val[t], vl);
  if (l == r)
    return;
  int mid = (l + r) >> 1;
  if (pos <= mid)
    insert(LD, l, mid, pos, vl);
  else
    insert(RD, mid + 1, r, pos, vl);
}

int query(int t, int l, int r, int ql, int qr) {
  if (ql > qr)
    return n + 1;
  if (ql <= l && r <= qr)
    return val[t];
  int mid = (l + r) >> 1, res = n + 1;
  if (ql <= mid)
    res = min(res, query(LD, l, mid, ql, qr));
  if (qr > mid)
    res = min(res, query(RD, mid + 1, r, ql, qr));
  return res;
}

int main() {
  scanf("%d %d", &n, &k);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    pos[a[i]] = i;
  }
  build(1, 1, n);
  // for (int i = 1; i <= n; i++) {
  //   printf("%d ", pos[i]);
  // }
  // puts("");
  for (int i = n; i >= 1; i--) {
    int l = query(1, 1, n, max(1, pos[i] - k + 1), pos[i] - 1);
    int r = query(1, 1, n, pos[i] + 1, min(n, pos[i] + k - 1));
    // cout<<i<<" "<<l<<" "<<r<<endl;
    if (r <= n) {
      g[pos[i]].push_back(pos[r]);
      deg[pos[r]]++;
    }
    if (l <= n) {
      g[pos[i]].push_back(pos[l]);
      deg[pos[l]]++;
    }
    insert(1, 1, n, pos[i], i);
  }
  int cur = 0;
  priority_queue<int, vector<int>, greater<int>> q;
  for (int i = 1; i <= n; i++) {
    if (!deg[i]) {
      q.push(i);
    }
  }
  while (q.size()) {
    int u = q.top();
    q.pop();
    ans[u] = ++cur;
    for (auto v : g[u]) {
      if (!(--deg[v])) {
        q.push(v);
      }
    }
  }
  for (int i = 1; i <= n; i++) {
    printf("%d\n", ans[i]);
  }
  return 0;
}