Problem p01707 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <algorithm>
#include <bits/stdc++.h>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <string>
#include <vector>
//    #include <boost/multiprecision/cpp_int.hpp>
#include <functional>
#define int long long
#define inf 1000000007
#define pa pair<int, int>
#define ll long long
#define pal pair<double, pa>
#define ppap pair<pa, int>

#define ssa pair<string, int>
#define mp make_pair
#define pb push_back
#define EPS (1e-10)
#define equals(a, b) (fabs((a) - (b)) < EPS)
int dx[4] = {0, -1, 0, 1};
int dy[4] = {1, 0, -1, 0};
using namespace std;
class pa3 {
public:
  int x, y, z;
  pa3(int x = 0, int y = 0, int z = 0) : x(x), y(y), z(z) {}
  bool operator<(const pa3 &p) const {
    if (x != p.x)
      return x < p.x;
    if (y != p.y)
      return y < p.y;
    return z < p.z;
    // return x != p.x ? x<p.x: y<p.y;
  }
  bool operator==(const pa3 &p) const {
    return x == p.x && y == p.y && z == p.z;
  }
};

class pa4 {
public:
  double x;
  int y, z, w;
  pa4(double x = 0, int y = 0, int z = 0, int w = 0) : x(x), y(y), z(z), w(w) {}
  bool operator<(const pa4 &p) const {
    if (x != p.x)
      return x < p.x;
    if (y != p.y)
      return y < p.y;
    if (z != p.z)
      return z < p.z;
    return w < p.w;
    // return x != p.x ? x<p.x: y<p.y;
  }
  bool operator>(const pa4 &p) const {
    if (x != p.x)
      return x > p.x;
    if (y != p.y)
      return y > p.y;
    if (z != p.z)
      return z > p.z;
    return w > p.w;
    // return x != p.x ? x<p.x: y<p.y;
  }
  bool operator==(const pa4 &p) const {
    return x == p.x && y == p.y && z == p.z && w == p.w;
  }
};
class pa2 {
public:
  int x, y;
  pa2(int x = 0, int y = 0) : x(x), y(y) {}
  pa2 operator+(pa2 p) { return pa2(x + p.x, y + p.y); }
  pa2 operator-(pa2 p) { return pa2(x - p.x, y - p.y); }
  bool operator<(const pa2 &p) const { return x != p.x ? x < p.x : y < p.y; }
  bool operator==(const pa2 &p) const {
    return abs(x - p.x) == 0 && abs(y - p.y) == 0;
  }
  bool operator!=(const pa2 &p) const {
    return !(abs(x - p.x) == 0 && abs(y - p.y) == 0);
  }
};

#define ppa pair<int, pas>
class Point {
public:
  double x, y;
  Point(double x = 0, double y = 0) : x(x), y(y) {}
  Point operator+(Point p) { return Point(x + p.x, y + p.y); }
  Point operator-(Point p) { return Point(x - p.x, y - p.y); }
  Point operator*(double a) { return Point(x * a, y * a); }
  Point operator/(double a) { return Point(x / a, y / a); }
  double absv() { return sqrt(norm()); }
  double norm() { return x * x + y * y; }
  bool operator<(const Point &p) const { return x != p.x ? x < p.x : y < p.y; }
  bool operator==(const Point &p) const {
    return fabs(x - p.x) < EPS && fabs(y - p.y) < EPS;
  }
};
typedef Point Vector;
#define pl pair<int, pas>
struct Segment {
  Point p1, p2;
};
double dot(Vector a, Vector b) { return a.x * b.x + a.y * b.y; }
double cross(Vector a, Vector b) { return a.x * b.y - a.y * b.x; }

bool parareru(Point a, Point b, Point c, Point d) {
  //	if(abs(cross(a-b,d-c))<EPS)cout<<"dd "<<cross(a-b,d-c)<<endl;
  return abs(cross(a - b, d - c)) < EPS;
}
double distance_ls_p(Point a, Point b, Point c) {
  if (dot(b - a, c - a) < EPS)
    return (c - a).absv();
  if (dot(a - b, c - b) < EPS)
    return (c - b).absv();
  return abs(cross(b - a, c - a)) / (b - a).absv();
}
bool is_intersected_ls(Segment a, Segment b) {
  if (a.p1 == b.p1 || a.p2 == b.p1 || a.p1 == b.p2 || a.p2 == b.p2)
    return false;
  if (parareru((a.p2), (a.p1), (a.p1), (b.p2)) &&
      parareru((a.p2), (a.p1), (a.p1), (b.p1))) {
    //		cout<<"sss"<<endl;
    if (dot(a.p1 - b.p1, a.p1 - b.p2) < EPS)
      return true;
    if (dot(a.p2 - b.p1, a.p2 - b.p2) < EPS)
      return true;
    if (dot(a.p1 - b.p1, a.p2 - b.p1) < EPS)
      return true;
    if (dot(a.p1 - b.p2, a.p2 - b.p2) < EPS)
      return true;
    return false;
  } else
    return (cross(a.p2 - a.p1, b.p1 - a.p1) * cross(a.p2 - a.p1, b.p2 - a.p1) <
            EPS) &&
           (cross(b.p2 - b.p1, a.p1 - b.p1) * cross(b.p2 - b.p1, a.p2 - b.p1) <
            EPS);
}

double segment_dis(Segment a, Segment b) {
  if (is_intersected_ls(a, b))
    return 0;
  double r = distance_ls_p(a.p1, a.p2, b.p1);
  r = min(r, distance_ls_p(a.p1, a.p2, b.p2));
  r = min(r, distance_ls_p(b.p1, b.p2, a.p2));
  r = min(r, distance_ls_p(b.p1, b.p2, a.p1));
  return r;
}
Point intersection_ls(Segment a, Segment b) {
  Point ba = b.p2 - b.p1;
  double d1 = abs(cross(ba, a.p1 - b.p1));
  double d2 = abs(cross(ba, a.p2 - b.p1));
  double t = d1 / (d1 + d2);

  return a.p1 + (a.p2 - a.p1) * t;
}

string itos(int i) {
  ostringstream s;
  s << i;
  return s.str();
}

int gcd(int v, int b) {
  if (v > b)
    return gcd(b, v);
  if (v == b)
    return b;
  if (b % v == 0)
    return v;
  return gcd(v, b % v);
}

double distans(double x1, double y1, double x2, double y2) {
  double rr = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
  return sqrt(rr);
}

//         int pr[2000010];
//       int inv[2000010];

int beki(int wa, int rr, int warukazu) {
  if (rr == 0)
    return 1ll;
  if (rr == 1)
    return wa % warukazu;
  if (rr % 2 == 1)
    return (beki(wa, rr - 1, warukazu) * wa) % warukazu;
  int zx = beki(wa, rr / 2, warukazu);
  return (zx * zx) % warukazu;
}
/*
            int comb(int nn,int rr){
                    int r=pr[nn]*inv[rr];
                    r%=inf;
                    r*=inv[nn-rr];
                    r%=inf;
                    return r;
            }

void gya(int ert){
    pr[0]=1;
    for(int i=1;i<ert;i++){
            pr[i]=(pr[i-1]*i)%inf;
    }
    for(int i=0;i<ert;i++) inv[i]=beki(pr[i],inf-2,inf);

}
 */

// sort(ve.begin(),ve.end(),greater<int>());
//----------------kokomade tenpure------------
// vector<double> ans(100000000),ans2(100000000);

int dp[2100][2100];

int cm(int r, int k) {
  int c = 1;
  for (int i = r; i >= r - k + 1; i--) {
    c *= (i % inf);
    c %= inf;
  }
  for (int i = 1; i <= k; i++) {
    c *= beki(i, inf - 2, inf);
    c %= inf;
  }
  return c;
}

signed main() {
  int n, d, x;

  while (1) {
    //	return 0;
    int m, n;
    cin >> n >> d >> x;

    if (n == 0)
      return 0;

    for (int i = 0; i < 2100; i++)
      for (int j = 0; j < 2100; j++)
        dp[i][j] = 0;
    dp[0][0] = 1;

    for (int i = 1; i <= n; i++)
      for (int j = i; j <= n; j++) {
        if (j >= x)
          dp[i][j] = dp[i][j - 1] + dp[i - 1][j - 1] - dp[i - 1][j - x];
        else
          dp[i][j] = dp[i][j - 1] + dp[i - 1][j - 1];
        dp[i][j] += 10ll * inf;
        dp[i][j] %= inf;
        //		cout<<i<<" "<<j<<" "<<dp[i][j]<<endl;
      }
    int ans = 0;

    int c[2100];
    c[1] = d % inf;
    for (int i = 2; i <= 2000; i++) {
      int rr = c[i - 1] * ((d - i + 1) % inf);
      rr %= inf;
      rr *= beki(i, inf - 2, inf);
      rr %= inf;
      c[i] = rr;
    }
    for (int i = 1; i <= min(n, d); i++) {
      //		cout<<dp[i][n]<<endl;
      ans += (dp[i][n] * c[i]) % inf;
      ans %= inf;
    }
    cout << ans << endl;
  }
  return 0;
}


Error: TLE

Fixed submission:

#include <algorithm>
#include <bits/stdc++.h>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <string>
#include <vector>
//    #include <boost/multiprecision/cpp_int.hpp>
#include <functional>
#define int long long
#define inf 1000000007
#define pa pair<int, int>
#define ll long long
#define pal pair<double, pa>
#define ppap pair<pa, int>

#define ssa pair<string, int>
#define mp make_pair
#define pb push_back
#define EPS (1e-10)
#define equals(a, b) (fabs((a) - (b)) < EPS)
int dx[4] = {0, -1, 0, 1};
int dy[4] = {1, 0, -1, 0};
using namespace std;
class pa3 {
public:
  int x, y, z;
  pa3(int x = 0, int y = 0, int z = 0) : x(x), y(y), z(z) {}
  bool operator<(const pa3 &p) const {
    if (x != p.x)
      return x < p.x;
    if (y != p.y)
      return y < p.y;
    return z < p.z;
    // return x != p.x ? x<p.x: y<p.y;
  }
  bool operator==(const pa3 &p) const {
    return x == p.x && y == p.y && z == p.z;
  }
};

class pa4 {
public:
  double x;
  int y, z, w;
  pa4(double x = 0, int y = 0, int z = 0, int w = 0) : x(x), y(y), z(z), w(w) {}
  bool operator<(const pa4 &p) const {
    if (x != p.x)
      return x < p.x;
    if (y != p.y)
      return y < p.y;
    if (z != p.z)
      return z < p.z;
    return w < p.w;
    // return x != p.x ? x<p.x: y<p.y;
  }
  bool operator>(const pa4 &p) const {
    if (x != p.x)
      return x > p.x;
    if (y != p.y)
      return y > p.y;
    if (z != p.z)
      return z > p.z;
    return w > p.w;
    // return x != p.x ? x<p.x: y<p.y;
  }
  bool operator==(const pa4 &p) const {
    return x == p.x && y == p.y && z == p.z && w == p.w;
  }
};
class pa2 {
public:
  int x, y;
  pa2(int x = 0, int y = 0) : x(x), y(y) {}
  pa2 operator+(pa2 p) { return pa2(x + p.x, y + p.y); }
  pa2 operator-(pa2 p) { return pa2(x - p.x, y - p.y); }
  bool operator<(const pa2 &p) const { return x != p.x ? x < p.x : y < p.y; }
  bool operator==(const pa2 &p) const {
    return abs(x - p.x) == 0 && abs(y - p.y) == 0;
  }
  bool operator!=(const pa2 &p) const {
    return !(abs(x - p.x) == 0 && abs(y - p.y) == 0);
  }
};

#define ppa pair<int, pas>
class Point {
public:
  double x, y;
  Point(double x = 0, double y = 0) : x(x), y(y) {}
  Point operator+(Point p) { return Point(x + p.x, y + p.y); }
  Point operator-(Point p) { return Point(x - p.x, y - p.y); }
  Point operator*(double a) { return Point(x * a, y * a); }
  Point operator/(double a) { return Point(x / a, y / a); }
  double absv() { return sqrt(norm()); }
  double norm() { return x * x + y * y; }
  bool operator<(const Point &p) const { return x != p.x ? x < p.x : y < p.y; }
  bool operator==(const Point &p) const {
    return fabs(x - p.x) < EPS && fabs(y - p.y) < EPS;
  }
};
typedef Point Vector;
#define pl pair<int, pas>
struct Segment {
  Point p1, p2;
};
double dot(Vector a, Vector b) { return a.x * b.x + a.y * b.y; }
double cross(Vector a, Vector b) { return a.x * b.y - a.y * b.x; }

bool parareru(Point a, Point b, Point c, Point d) {
  //	if(abs(cross(a-b,d-c))<EPS)cout<<"dd "<<cross(a-b,d-c)<<endl;
  return abs(cross(a - b, d - c)) < EPS;
}
double distance_ls_p(Point a, Point b, Point c) {
  if (dot(b - a, c - a) < EPS)
    return (c - a).absv();
  if (dot(a - b, c - b) < EPS)
    return (c - b).absv();
  return abs(cross(b - a, c - a)) / (b - a).absv();
}
bool is_intersected_ls(Segment a, Segment b) {
  if (a.p1 == b.p1 || a.p2 == b.p1 || a.p1 == b.p2 || a.p2 == b.p2)
    return false;
  if (parareru((a.p2), (a.p1), (a.p1), (b.p2)) &&
      parareru((a.p2), (a.p1), (a.p1), (b.p1))) {
    //		cout<<"sss"<<endl;
    if (dot(a.p1 - b.p1, a.p1 - b.p2) < EPS)
      return true;
    if (dot(a.p2 - b.p1, a.p2 - b.p2) < EPS)
      return true;
    if (dot(a.p1 - b.p1, a.p2 - b.p1) < EPS)
      return true;
    if (dot(a.p1 - b.p2, a.p2 - b.p2) < EPS)
      return true;
    return false;
  } else
    return (cross(a.p2 - a.p1, b.p1 - a.p1) * cross(a.p2 - a.p1, b.p2 - a.p1) <
            EPS) &&
           (cross(b.p2 - b.p1, a.p1 - b.p1) * cross(b.p2 - b.p1, a.p2 - b.p1) <
            EPS);
}

double segment_dis(Segment a, Segment b) {
  if (is_intersected_ls(a, b))
    return 0;
  double r = distance_ls_p(a.p1, a.p2, b.p1);
  r = min(r, distance_ls_p(a.p1, a.p2, b.p2));
  r = min(r, distance_ls_p(b.p1, b.p2, a.p2));
  r = min(r, distance_ls_p(b.p1, b.p2, a.p1));
  return r;
}
Point intersection_ls(Segment a, Segment b) {
  Point ba = b.p2 - b.p1;
  double d1 = abs(cross(ba, a.p1 - b.p1));
  double d2 = abs(cross(ba, a.p2 - b.p1));
  double t = d1 / (d1 + d2);

  return a.p1 + (a.p2 - a.p1) * t;
}

string itos(int i) {
  ostringstream s;
  s << i;
  return s.str();
}

int gcd(int v, int b) {
  if (v > b)
    return gcd(b, v);
  if (v == b)
    return b;
  if (b % v == 0)
    return v;
  return gcd(v, b % v);
}

double distans(double x1, double y1, double x2, double y2) {
  double rr = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
  return sqrt(rr);
}

//         int pr[2000010];
//       int inv[2000010];

int beki(int wa, int rr, int warukazu) {
  if (rr == 0)
    return 1ll;
  if (rr == 1)
    return wa % warukazu;
  if (rr % 2 == 1)
    return (beki(wa, rr - 1, warukazu) * wa) % warukazu;
  int zx = beki(wa, rr / 2, warukazu);
  return (zx * zx) % warukazu;
}
/*
            int comb(int nn,int rr){
                    int r=pr[nn]*inv[rr];
                    r%=inf;
                    r*=inv[nn-rr];
                    r%=inf;
                    return r;
            }

void gya(int ert){
    pr[0]=1;
    for(int i=1;i<ert;i++){
            pr[i]=(pr[i-1]*i)%inf;
    }
    for(int i=0;i<ert;i++) inv[i]=beki(pr[i],inf-2,inf);

}
 */

// sort(ve.begin(),ve.end(),greater<int>());
//----------------kokomade tenpure------------
// vector<double> ans(100000000),ans2(100000000);

int dp[2100][2100];

int cm(int r, int k) {
  int c = 1;
  for (int i = r; i >= r - k + 1; i--) {
    c *= i;
    c %= inf;
  }
  for (int i = 1; i <= k; i++) {
    c *= beki(i, inf - 2, inf);
    c %= inf;
  }
  return c;
}

signed main() {
  int n, d, x;

  while (1) {
    //	return 0;
    int m, n;
    cin >> n >> d >> x;

    if (n == 0)
      return 0;

    for (int i = 0; i < 2100; i++)
      for (int j = 0; j < 2100; j++)
        dp[i][j] = 0;
    dp[0][0] = 1;

    for (int i = 1; i <= n; i++)
      for (int j = i; j <= n; j++) {
        if (j >= x)
          dp[i][j] = dp[i][j - 1] + dp[i - 1][j - 1] - dp[i - 1][j - x];
        else
          dp[i][j] = dp[i][j - 1] + dp[i - 1][j - 1];
        dp[i][j] += 10ll * inf;
        dp[i][j] %= inf;
        //		cout<<i<<" "<<j<<" "<<dp[i][j]<<endl;
      }
    int ans = 0;
    for (int i = 1; i <= min(n, d); i++) {
      //		cout<<dp[i][n]<<endl;
      ans += (dp[i][n] * cm(d, i)) % inf;
      ans %= inf;
    }
    cout << ans << endl;
  }
  return 0;
}