Problem p03782 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = int(a); i < int(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = int(a) - 1; i >= int(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))
#define popcount(n) (__builtin_popcountll(n))

using namespace std;

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using ll = long long;
using R = long double;
const R EPS = 1e-9L; // [-1000,1000]->EPS=1e-8 [-10000,10000]->EPS=1e-7
inline int sgn(const R &r) { return (r > EPS) - (r < -EPS); }
inline R sq(R x) { return sqrt(max(x, 0.0L)); }

const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};

// Problem Specific Parameter:

int n, k;
int a[5010];

bool per[5010][5010], rev[5010][5010];

int main(void) {
  cin >> n >> k;
  rep(i, n) cin >> a[i];

  per[0][0] = true;
  rep(i, n) rep(j, k + 1) {
    if (per[i][j] == false)
      continue;
    per[i + 1][j] = true;
    if (j + a[i] <= k)
      per[i + 1][j + a[i]] = true;
  }

  rev[n][0] = true;
  rrep(i, n) rep(j, k + 1) {
    if (rev[i + 1][j] == false)
      continue;
    rev[i][j] = true;
    if (j + a[i] <= k)
      rev[i][j + a[i]] = true;
  }

  int ans = 0;
  rep(i, n) {
    set<int> s;
    rep(j, k + 1) if (rev[i + 1][j]) s.insert(j);
    bool ok = false;

    //[k-a[i],k-1]
    //[small,large]
    //[small-j,large-j]
    rep(j, k + 1) {
      if (per[i][j] == false)
        continue;
      auto it = s.lower_bound(k - a[i] - j);
      if (it != end(s) and *it <= k - 1 - j)
        ok = true;
    }

    if (ok == false)
      ans++;
  }

  cout << ans << endl;

  return 0;
}

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

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = int(a); i < int(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = int(a) - 1; i >= int(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))
#define popcount(n) (__builtin_popcountll(n))

using namespace std;

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using ll = long long;
using R = long double;
const R EPS = 1e-9L; // [-1000,1000]->EPS=1e-8 [-10000,10000]->EPS=1e-7
inline int sgn(const R &r) { return (r > EPS) - (r < -EPS); }
inline R sq(R x) { return sqrt(max(x, 0.0L)); }

const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};

// Problem Specific Parameter:

int n, k;
int a[5010];

bool per[5010][5010], rev[5010][5010];

int main(void) {
  cin >> n >> k;
  rep(i, n) cin >> a[i];

  sort(a, a + n);

  {
    int limit = 0;
    rep(i, n) if (a[i] <= k) limit = i;
    n = limit + 1;
  }

  per[0][0] = true;
  rep(i, n) rep(j, k + 1) {
    if (per[i][j] == false)
      continue;
    per[i + 1][j] = true;
    if (j + a[i] <= k)
      per[i + 1][j + a[i]] = true;
  }

  rev[n][0] = true;
  rrep(i, n) rep(j, k + 1) {
    if (rev[i + 1][j] == false)
      continue;
    rev[i][j] = true;
    if (j + a[i] <= k)
      rev[i][j + a[i]] = true;
  }

  int ans = 0;
  rep(i, n) {
    set<int> s;
    rep(j, k + 1) if (rev[i + 1][j]) s.insert(j);
    bool ok = false;

    //[k-a[i],k-1]
    //[small,large]
    //[small-j,large-j]
    rep(j, k + 1) {
      if (per[i][j] == false)
        continue;
      auto it = s.lower_bound(k - a[i] - j);
      if (it != end(s) and *it <= k - 1 - j)
        ok = true;
    }

    if (ok == false)
      ans++;
  }

  cout << ans << endl;

  return 0;
}