Problem p00892 (C++)

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

using namespace std;

#define rep(i, n) for (int i = 0; i < int(n); ++i)

const int DIV = 1000000;

int m, n;
double x1[100], y[100], x2[100], z[100];
double mnx, mxx;

double solve(double x) {
  double y1 = 0, y2 = 0, z1 = 0, z2 = 0;
  static int px11 = 0, px12 = 0, px21 = 0, px22 = 0;
  rep(ii, m) {
    int i = (px11 + ii) % m;
    if (x1[i] != x1[(i + 1) % m] && x1[i] <= x && x <= x1[(i + 1) % m]) {
      y1 = y[i] +
           (y[(i + 1) % m] - y[i]) / (x1[(i + 1) % m] - x1[i]) * (x - x1[i]);
      px11 = i;
      break;
    }
  }
  rep(ii, m) {
    int i = (px12 - ii + m) % m;
    if (x1[i] != x1[(i + 1) % m] && x1[(i + 1) % m] <= x && x <= x1[i]) {
      y2 = y[i] +
           (y[(i + 1) % m] - y[i]) / (x1[(i + 1) % m] - x1[i]) * (x - x1[i]);
      px12 = i;
      break;
    }
  }
  rep(ii, n) {
    int i = (px21 + ii) % n;
    if (x2[i] != x2[(i + 1) % n] && x2[i] <= x && x <= x2[(i + 1) % n]) {
      z1 = z[i] +
           (z[(i + 1) % n] - z[i]) / (x2[(i + 1) % n] - x2[i]) * (x - x2[i]);
      px21 = i;
      break;
    }
  }
  rep(ii, n) {
    int i = (px22 - ii + n) % n;
    if (x2[i] != x2[(i + 1) % n] && x2[(i + 1) % n] <= x && x <= x2[i]) {
      z2 = z[i] +
           (z[(i + 1) % n] - z[i]) / (x2[(i + 1) % n] - x2[i]) * (x - x2[i]);
      px22 = i;
      break;
    }
  }
  return (y2 - y1) * (z2 - z1);
}

double simpson(double l, double r, double f(double), int k = 1) {
  double h = (r - l) / (2 * k);
  double fo = 0, fe = 0;
  for (int i = 1; i <= 2 * k - 3; i += 2) {
    fo += f(l + h * i);
    fe += f(l + h * (i + 1));
  }
  return (f(l) + f(r) + 4 * (fo + f(r - h)) + 2 * fe) * h / 3;
}

int main() {
  while (true) {
    cin >> m >> n;
    if (m == 0 && n == 0)
      break;
    rep(i, m) cin >> x1[i] >> y[i];
    rep(i, n) cin >> x2[i] >> z[i];
    double mnx = max(*min_element(x1, x1 + m), *min_element(x2, x2 + n));
    double mxx = min(*max_element(x1, x1 + m), *max_element(x2, x2 + n));
    printf("%.12lf\n", simpson(mnx, mxx, solve, DIV));
  }
}

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

using namespace std;

#define rep(i, n) for (int i = 0; i < int(n); ++i)

const int DIV = 500000;

int m, n;
double x1[100], y[100], x2[100], z[100];
double mnx, mxx;

double solve(double x) {
  double y1 = 0, y2 = 0, z1 = 0, z2 = 0;
  static int px11 = 0, px12 = 0, px21 = 0, px22 = 0;
  rep(ii, m) {
    int i = (px11 + ii) % m;
    if (x1[i] != x1[(i + 1) % m] && x1[i] <= x && x <= x1[(i + 1) % m]) {
      y1 = y[i] +
           (y[(i + 1) % m] - y[i]) / (x1[(i + 1) % m] - x1[i]) * (x - x1[i]);
      px11 = i;
      break;
    }
  }
  rep(ii, m) {
    int i = (px12 - ii + m) % m;
    if (x1[i] != x1[(i + 1) % m] && x1[(i + 1) % m] <= x && x <= x1[i]) {
      y2 = y[i] +
           (y[(i + 1) % m] - y[i]) / (x1[(i + 1) % m] - x1[i]) * (x - x1[i]);
      px12 = i;
      break;
    }
  }
  rep(ii, n) {
    int i = (px21 + ii) % n;
    if (x2[i] != x2[(i + 1) % n] && x2[i] <= x && x <= x2[(i + 1) % n]) {
      z1 = z[i] +
           (z[(i + 1) % n] - z[i]) / (x2[(i + 1) % n] - x2[i]) * (x - x2[i]);
      px21 = i;
      break;
    }
  }
  rep(ii, n) {
    int i = (px22 - ii + n) % n;
    if (x2[i] != x2[(i + 1) % n] && x2[(i + 1) % n] <= x && x <= x2[i]) {
      z2 = z[i] +
           (z[(i + 1) % n] - z[i]) / (x2[(i + 1) % n] - x2[i]) * (x - x2[i]);
      px22 = i;
      break;
    }
  }
  return (y2 - y1) * (z2 - z1);
}

double simpson(double l, double r, double f(double), int k = 1) {
  double h = (r - l) / (2 * k);
  double fo = 0, fe = 0;
  for (int i = 1; i <= 2 * k - 3; i += 2) {
    fo += f(l + h * i);
    fe += f(l + h * (i + 1));
  }
  return (f(l) + f(r) + 4 * (fo + f(r - h)) + 2 * fe) * h / 3;
}

int main() {
  while (true) {
    cin >> m >> n;
    if (m == 0 && n == 0)
      break;
    rep(i, m) cin >> x1[i] >> y[i];
    rep(i, n) cin >> x2[i] >> z[i];
    double mnx = max(*min_element(x1, x1 + m), *min_element(x2, x2 + n));
    double mxx = min(*max_element(x1, x1 + m), *max_element(x2, x2 + n));
    printf("%.12lf\n", simpson(mnx, mxx, solve, DIV));
  }
}