Problem p03771 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define inf 0x3f3f3f3f
#define N 200010
inline int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-')
      f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9')
    x = x * 10 + ch - '0', ch = getchar();
  return x * f;
}
int n, v, tot = -1, bin[20], R[20][N], num[20], f1[N], f2[N],
          a[N]; // R[i][k],第i层的第k条线段的右端点
// num[i],第i层的线段条数 f1[s],选择s状态的层数,左边从1开始最远能覆盖到哪里
int main() {
  //	freopen("a.in","r",stdin);
  n = read();
  v = read();
  bin[0] = 1;
  for (int i = 1; i <= 20; ++i)
    bin[i] = bin[i - 1] << 1;
  for (int i = 1; i <= n; ++i)
    a[i] = read();
  int x = v * 2;
  while (x) {
    x /= 2;
    tot++;
    for (int i = 1; i <= n - 1; ++i) {
      if (a[i + 1] - a[i] <= x)
        continue;
      R[tot][++num[tot]] = i;
    }
    R[tot][++num[tot]] = n;
  }
  if (num[0] > tot + 1) {
    for (int i = 1; i <= n; ++i)
      puts("Impossible");
    return 0;
  }
  for (int s = 0; s <= bin[tot] - 1; ++s)
    f2[s] = n + 1;
  for (int s = 0; s <= bin[tot] - 1; ++s)
    for (int i = 1; i <= tot; ++i) {
      if (s & bin[i - 1])
        continue;
      f1[s | bin[i - 1]] = max(
          f1[s | bin[i - 1]], *upper_bound(R[i] + 1, R[i] + num[i] + 1, f1[s]));
      f2[s | bin[i - 1]] = min(
          f2[s | bin[i - 1]],
          R[i][lower_bound(R[i] + 1, R[i] + num[i] + 1, f2[s] - 1) - R[i] - 1] +
              1);
    }
  for (int i = 1; i <= num[0]; ++i) {
    bool flag = 0;
    for (int s = 0; s <= bin[tot] - 1; ++s)
      if (f1[s] >= R[0][i - 1] && f2[bin[tot] - 1 - s] <= R[0][i] + 1) {
        flag = 1;
        break;
      }
    for (int j = R[0][i - 1] + 1; j <= R[0][i]; ++j)
      puts(flag ? "Possible" : "Impossible");
  }
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define inf 0x3f3f3f3f
#define N 200010
inline int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (ch < '0' || ch > '9') {
    if (ch == '-')
      f = -1;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9')
    x = x * 10 + ch - '0', ch = getchar();
  return x * f;
}
int n, v, tot = -1, bin[22], R[22][N], num[22], f1[N << 3], f2[N << 3],
          a[N]; // R[i][k],第i层的第k条线段的右端点
// num[i],第i层的线段条数 f1[s],选择s状态的层数,左边从1开始最远能覆盖到哪里
int main() {
  //	freopen("a.in","r",stdin);
  n = read();
  v = read();
  bin[0] = 1;
  for (int i = 1; i <= 20; ++i)
    bin[i] = bin[i - 1] << 1;
  for (int i = 1; i <= n; ++i)
    a[i] = read();
  int x = v * 2;
  while (x) {
    x /= 2;
    tot++;
    for (int i = 1; i <= n - 1; ++i) {
      if (a[i + 1] - a[i] <= x)
        continue;
      R[tot][++num[tot]] = i;
    }
    R[tot][++num[tot]] = n;
  }
  if (num[0] > tot + 1) {
    for (int i = 1; i <= n; ++i)
      puts("Impossible");
    return 0;
  }
  for (int s = 0; s <= bin[tot] - 1; ++s)
    f2[s] = n + 1;
  for (int s = 0; s <= bin[tot] - 1; ++s)
    for (int i = 1; i <= tot; ++i) {
      if (s & bin[i - 1])
        continue;
      f1[s | bin[i - 1]] = max(
          f1[s | bin[i - 1]], *upper_bound(R[i] + 1, R[i] + num[i] + 1, f1[s]));
      f2[s | bin[i - 1]] = min(
          f2[s | bin[i - 1]],
          R[i][lower_bound(R[i] + 1, R[i] + num[i] + 1, f2[s] - 1) - R[i] - 1] +
              1);
    }
  for (int i = 1; i <= num[0]; ++i) {
    bool flag = 0;
    for (int s = 0; s <= bin[tot] - 1; ++s)
      if (f1[s] >= R[0][i - 1] && f2[bin[tot] - 1 - s] <= R[0][i] + 1) {
        flag = 1;
        break;
      }
    for (int j = R[0][i - 1] + 1; j <= R[0][i]; ++j)
      puts(flag ? "Possible" : "Impossible");
  }
  return 0;
}