Problem p02648 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <complex>
#include <cstdio>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>

#define REP(i, m, n) for (int i = int(m); i < int(n); i++)
#define RREP(i, m, n) for (int i = int(n) - 1; i >= int(m); --i)
#define EACH(i, c) for (auto &(i) : c)
#define all(c) begin(c), end(c)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort(begin(c), end(c))
#define pb emplace_back
#define MP make_pair
#define SZ(a) int((a).size())
// #define int long long

#ifdef LOCAL
#define DEBUG(s) cout << (s) << endl
#define dump(x) cerr << #x << " = " << (x) << endl
#define BR cout << endl;
#else
#define DEBUG(s)                                                               \\
  do {                                                                         \\
  } while (0)
#define dump(x)                                                                \\
  do {                                                                         \\
  } while (0)
#define BR
#endif
using namespace std;

using UI = unsigned int;
using UL = unsigned long;
using LL = long long;
using ULL = unsigned long long;
using VI = vector<int>;
using VVI = vector<VI>;
using VLL = vector<LL>;
using VVLL = vector<VLL>;
using VS = vector<string>;
using PII = pair<int, int>;
using VP = vector<PII>;
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}

void solve() {
  LL n, q;
  cin >> n;
  VLL v(n), w(n);
  REP(i, 0, n) cin >> v[i] >> w[i];
  cin >> q;

  VVLL as(512, VLL(100000 + 1));
  REP(k, 0, 512) {
    int u = k + 511;
    if (u >= n)
      break;
    VI ps;
    while (u > 0) {
      ps.push_back(u);
      u = (u - 1) / 2;
    }
    ps.push_back(0);
    int len = ps.size();
    REP(p, 0, 1 << len) {
      LL sumw = 0, sumv = 0;
      REP(j, 0, len) {
        if (!(p & (1 << j)))
          continue;
        sumw += w[ps[j]];
        sumv += v[ps[j]];
      }
      if (sumw > 100000)
        continue;
      chmax(as[k][sumw], sumv);
    }
    REP(i, 1, 100000 + 1) chmax(as[k][i], as[k][i - 1]);
  }

  int u, l;
  REP(z, 0, q) {
    cin >> u >> l;
    --u;
    LL ans = 0;
    if (u < 1023) {
      VI ps;
      while (u > 0) {
        ps.push_back(u);
        u = (u - 1) / 2;
      }
      ps.push_back(0);
      int len = ps.size();
      VLL minv(l + 1, 0);
      REP(p, 0, 1 << (len - len / 2)) {
        LL sumw = 0, sumv = 0;
        REP(j, 0, len - len / 2) {
          if (!(p & (1 << j)))
            continue;
          sumw += w[ps[j + len / 2]];
          sumv += v[ps[j + len / 2]];
        }
        if (sumw > l)
          continue;
        chmax(minv[sumw], sumv);
      }
      REP(i, 1, l + 1) chmax(minv[i], minv[i - 1]);

      // REP(i,0,l+1) cout << minv[i] << " ";
      // cout << endl;

      REP(p, 0, 1 << (len / 2)) {
        LL sumw = 0, sumv = 0;
        REP(j, 0, len / 2) {
          if (!(p & (1 << j)))
            continue;
          sumw += w[ps[j]];
          sumv += v[ps[j]];
        }
        if (sumw > l)
          continue;
        chmax(ans, sumv + minv[l - sumw]);
      }
    } else {
      VI ps;
      while (u > 1022) {
        ps.push_back(u);
        u = (u - 1) / 2;
      }
      int len = ps.size();
      REP(p, 0, 1 << (len)) {
        LL sumw = 0, sumv = 0;
        REP(j, 0, len) {
          if (!(p & (1 << j)))
            continue;
          sumw += w[ps[j]];
          sumv += v[ps[j]];
        }
        if (sumw > l)
          continue;
        chmax(ans, sumv + as[u - 511][l - sumw]);
      }
    }
    cout << ans << endl;
  }
}

signed main() {
  solve();

  return 0;
}


Error: WA

Fixed submission:

#include <stdio.h>
#include <vector>
using namespace std;
vector<int> vec[50100];
bool vst[50100];
int mx = 0;
void dfs(int cur, int lv) {
  vst[cur] = true;
  mx = max(mx, lv);
  for (int nxt : vec[cur]) {
    if (vst[nxt] == false)
      dfs(nxt, lv + 1);
  }
  return;
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; ++i) {
    int a, b;
    scanf("%d %d", &a, &b);
    vec[a].push_back(b);
    vec[b].push_back(a);
  }
  int st;
  for (int i = 1; i <= n; ++i)
    if (vec[i].size() == 1) {
      st = i;
      break;
    }
  dfs(st, 1);
  int ans = 0;
  while (mx > 0) {
    mx /= 2;
    ans++;
  }
  printf("%d", ans);
  return 0;
}