Problem p01425 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

#define REP(i, n) for (int i = 0; i < n; ++i)
#define MP make_pair
#define PB push_back

typedef double DB;
typedef long long LL;

const DB EPS = 1e-8;
const DB PI = acos(-1);
const DB gg = 9.8;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;

inline void checkMin(int &a, int b) {
  if (b < a)
    a = b;
}

inline int sgn(double x) { return x < -EPS ? -1 : x > EPS; }

const int N = int(1e2) + 9;
int n, l[N], b[N], r[N], t[N];
int X, Y;
DB V;
int low;

inline DB y(DB a, DB x) {
  DB t = x / (V * cos(a));
  return V * sin(a) * t - 0.5 * gg * t * t;
}

inline DB getM(DB a) {
  DB t = V * sin(a) / gg;
  return V * cos(a) * t;
}

bool ck(DB a) {

  DB h = y(a, X);
  if (sgn(h - Y) < 0 || sgn(h - low) > 0)
    return false;
  DB mx = getM(a), my = y(a, mx);

  REP(i, n) {

    DB h1 = y(a, l[i]), h2 = y(a, r[i]);

    if (l[i] <= mx && mx <= r[i]) {
      if (!(h1 <= b[i] && h2 <= b[i] && my <= b[i] ||
            h1 >= t[i] && h2 >= t[i] && my >= t[i]))
        return false;
    } else {
      if (!(h1 <= b[i] && h2 <= b[i] || h1 >= t[i] && h2 >= t[i]))
        return false;
    }
  }
  return true;
}

bool ck() {

  REP(i, n) {
    if (l[i] == 0 && b[i] == 0)
      return false;
    if (l[i] <= X && X <= r[i] && b[i] <= Y && Y <= t[i])
      return false;
  }

  DB d = PI / 2 / 15000;
  for (DB a = d; a <= PI / 2; a += d)
    if (ck(a))
      return true;
  return false;
}

int main() {
  freopen("in.txt", "r", stdin);
  while (~scanf("%d%lf%d%d", &n, &V, &X, &Y)) {
    low = INF;
    REP(i, n) {
      scanf("%d%d%d%d", &l[i], &b[i], &r[i], &t[i]);
      if (l[i] > X) {
        --i;
        --n;
        continue;
      }
      if (r[i] >= X) {
        if (b[i] >= Y)
          checkMin(low, b[i]);
        r[i] = X;
      }
    }
    puts(ck() ? "Yes" : "No");
  }
}

Fixed submission:
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

#define REP(i, n) for (int i = 0; i < n; ++i)
#define MP make_pair
#define PB push_back

typedef double DB;
typedef long long LL;

const DB EPS = 1e-8;
const DB PI = acos(-1);
const DB gg = 9.8;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;

inline void checkMin(int &a, int b) {
  if (b < a)
    a = b;
}

inline int sgn(double x) { return x < -EPS ? -1 : x > EPS; }

const int N = int(1e2) + 9;
int n, l[N], b[N], r[N], t[N];
int X, Y;
DB V;
int low;

inline DB y(DB a, DB x) {
  DB t = x / (V * cos(a));
  return V * sin(a) * t - 0.5 * gg * t * t;
}

inline DB getM(DB a) {
  DB t = V * sin(a) / gg;
  return V * cos(a) * t;
}

bool ck(DB a) {

  DB h = y(a, X);
  if (sgn(h - Y) < 0 || sgn(h - low) > 0)
    return false;
  DB mx = getM(a), my = y(a, mx);

  REP(i, n) {

    DB h1 = y(a, l[i]), h2 = y(a, r[i]);

    if (l[i] <= mx && mx <= r[i]) {
      if (!(h1 <= b[i] && h2 <= b[i] && my <= b[i] ||
            h1 >= t[i] && h2 >= t[i] && my >= t[i]))
        return false;
    } else {
      if (!(h1 <= b[i] && h2 <= b[i] || h1 >= t[i] && h2 >= t[i]))
        return false;
    }
  }
  return true;
}

bool ck() {

  REP(i, n) {
    if (l[i] == 0 && b[i] == 0)
      return false;
    if (l[i] <= X && X <= r[i] && b[i] <= Y && Y <= t[i])
      return false;
  }

  DB d = PI / 2 / 15000;
  for (DB a = d; a <= PI / 2; a += d)
    if (ck(a))
      return true;
  return false;
}

int main() {
  //    freopen("in.txt", "r", stdin);
  while (~scanf("%d%lf%d%d", &n, &V, &X, &Y)) {
    low = INF;
    REP(i, n) {
      scanf("%d%d%d%d", &l[i], &b[i], &r[i], &t[i]);
      if (l[i] > X) {
        --i;
        --n;
        continue;
      }
      if (r[i] >= X) {
        if (b[i] >= Y)
          checkMin(low, b[i]);
        r[i] = X;
      }
    }
    puts(ck() ? "Yes" : "No");
  }
}