Problem p03794 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stdio.h>
#include <utility>
#include <vector>
using namespace std;
#define y0 y0z
#define y1 y1z
#define yn ynz
#define j0 j0z
#define j1 j1z
#define jn jnz
#define tm tmz
#define buli(x) (__builtin_popcountll(x))
#define bur0(x) (__builtin_ctzll(x))
#define bul2(x) (63 - __builtin_clzll(x))
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define fil(a, b) memset((a), (b), sizeof(a))
#define cl(a) fil(a, 0)
#define siz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define foreach(it, a)                                                         \\
  for (__typeof((a).begin()) it = (a).begin(); it != (a).end(); it++)
#define rep(i, a, b) for (int i = (a), _ed = (b); i < _ed; i++)
#define per(i, a, b) for (int i = (b)-1, _ed = (a); i >= _ed; i--)
#define forg(i, gu) for (int i = gu; ~i; i = e[i].next)
#define pw(x) ((ll(1)) << (x))
#define upmo(a, b) (((a) = ((a) + (b)) % mo) < 0 ? (a) += mo : (a))
#define mmo(a, b) (((a) = 1ll * (a) * (b) % mo) < 0 ? (a) += mo : (a))
void getre() {
  int x = 0;
  printf("%d\\n", 1 / x);
}
void gettle() {
  int res = 1;
  while (1)
    res <<= 1;
  printf("%d\\n", res);
}
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pii> vpii;
template <typename T, typename S> inline bool upmin(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T, typename S> inline bool upmax(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}
template <typename N, typename PN> inline N flo(N a, PN b) {
  return a >= 0 ? a / b : -((-a - 1) / b) - 1;
}
template <typename N, typename PN> inline N cei(N a, PN b) {
  return a > 0 ? (a - 1) / b + 1 : -(-a / b);
}
template <typename N> N gcd(N a, N b) { return b ? gcd(b, a % b) : a; }
template <typename N> inline int sgn(N a) {
  return a > 0 ? 1 : (a < 0 ? -1 : 0);
}
#if ((_WIN32 || __WIN32__) && __cplusplus < 201103L)
#define lld "%I64d"
#else
#define lld "%lld"
#endif
inline void gn(long long &x) {
  int sg = 1;
  char c;
  while (((c = getchar()) < '0' || c > '9') && c != '-')
    ;
  c == '-' ? (sg = -1, x = 0) : (x = c - '0');
  while ((c = getchar()) >= '0' && c <= '9')
    x = x * 10 + c - '0';
  x *= sg;
}
inline void gn(int &x) {
  long long t;
  gn(t);
  x = t;
}
inline void gn(unsigned long long &x) {
  long long t;
  gn(t);
  x = t;
}
inline void gn(double &x) {
  double t;
  scanf("%lf", &t);
  x = t;
}
inline void gn(long double &x) {
  double t;
  scanf("%lf", &t);
  x = t;
}
inline void gs(char *s) { scanf("%s", s); }
inline void gc(char &c) {
  while ((c = getchar()) > 126 || c < 33)
    ;
}
inline void pc(char c) { putchar(c); }
#ifdef JCVB
#define debug(...) fprintf(stderr, __VA_ARGS__)
#else
#define debug(...)
#endif
typedef long long ll;
typedef double db;
inline ll sqr(ll a) { return a * a; }
inline db sqrf(db a) { return a * a; }
const int inf = 0x3f3f3f3f;
// const ll inf=0x3f3f3f3f3f3f3f3fll;
const db pi = 3.14159265358979323846264338327950288L;
const db eps = 1e-6;
const int mo = 1e9 + 7;
// int qp(int a,ll b){int
// n=1;do{if(b&1)n=1ll*n*a%mo;a=1ll*a*a%mo;}while(b>>=1);return n;}

const int TREE_MAXV = 3000 + 5;
struct edge {
  int v, next;
} e[TREE_MAXV * 2];
int g[TREE_MAXV], etot;
int qu[TREE_MAXV], pre[TREE_MAXV];
int h[33333];
int n;
void ae(int u, int v) {
  e[etot].v = v;
  e[etot].next = g[u];
  g[u] = etot++;
}

int bel[33333];
void bfs(int rt) {
  int p = 0, q = 0;
  pre[rt] = 0;
  h[rt] = 0;
  qu[q++] = rt;
  while (p != q) {
    int u = qu[p++];
    for (int i = g[u]; ~i; i = e[i].next)
      if (e[i].v != pre[u]) {
        pre[e[i].v] = u;
        bel[e[i].v] |= bel[u];
        h[e[i].v] = h[u] + 1;
        qu[q++] = e[i].v;
      }
  }
}
void tree_init() {
  static bool ini = 0;
  if (!ini) {
    ini = 1;
    memset(g, -1, sizeof(g));
  } else {
    for (int i = 0; i <= n; i++)
      g[i] = -1;
  }
  etot = 0;
}
void readedge() {
  for (int i = 1; i < n; i++) {
    int x, y;
    gn(x);
    gn(y);
    ae(x, y);
    ae(y, x);
  }
}

int boun[2222], to[2222];
const int zer = 1111;
int f[1111][2222];

int dp() {
  cl(f);
  for (int i = n - 1; i >= 0; i--) {
    int u = qu[i];

    for (int j = to[u] - boun[u]; j <= to[u] + boun[u]; j++) {
      f[u][j + zer] = 1;
      forg(t, g[u]) if (e[t].v != pre[u])
          mmo(f[u][j + zer], (f[e[t].v][j - 1 + zer] + f[e[t].v][j + 1 + zer]));
    }
  }
  int ret = 0;
  rep(t, 0, 2222) upmo(ret, f[qu[0]][t]);
  return ret;
}

int main() {
#ifdef JCVB
  // freopen("1.in","r",stdin);
  // freopen("1.out","w",stdout);
  int _time_jc = clock();
#endif
  gn(n);
  tree_init();
  readedge();

  static int dis1[2222];

  bfs(1);
  int ma = 1;
  rep(u, 2, n + 1) if (h[u] > h[ma]) ma = u;
  bfs(ma);
  int mav = 1;
  rep(u, 1, n + 1) if (h[u] > h[mav]) mav = u;

  bfs(mav);
  rep(i, 1, n + 1) dis1[i] = h[i];
  bfs(ma);
  int r;

  r = cei(h[mav], 2);
  int rt = 0, rt2 = 0;

  if (h[mav] % 2 == 0) {
    rep(i, 1, n + 1) {
      if (dis1[i] == h[i] && h[i] == h[mav] / 2)
        rt = i;
    }
  } else {
    rep(i, 1, n + 1) {
      if (dis1[i] == h[mav] / 2 && h[i] == (h[mav] + 1) / 2)
        rt = i;
      if (dis1[i] == (h[mav] + 1) / 2 && h[i] == (h[mav] + 0) / 2)
        rt2 = i;
    }
  }

  bel[rt2] = 1;
  bfs(rt);

  int ans = 0;
  if (rt2 == 0) {
    rep(u, 1, n + 1) boun[u] = r - h[u], to[u] = 0;
    upmo(ans, dp());
  } else {
    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (bel[u]) {
        to[u] = 0;
        boun[u] = d;
      } else {
        to[u] = 0;
        boun[u] = d + 1;
      }
    }
    upmo(ans, dp());
    /* rep(u,1,n+1){ */
    /* 	int d; */
    /* 	if(!bel[u])d=r-1-h[u];else d=r-h[u]; */
    /* 	if(bel[u]){ */
    /* 		to[u]=0; */
    /* 		boun[u]=d; */
    /* 	}else{ */
    /* 		to[u]=0; */
    /* 		boun[u]=d+1; */
    /* 		if(d==0){ */
    /* 			to[u]=1; */
    /* 			boun[u]=0; */
    /* 		} */
    /* 	} */
    /* } */
    /* upmo(ans,-dp()); */

    /* rep(u,1,n+1){ */
    /* 	int d; */
    /* 	if(!bel[u])d=r-1-h[u];else d=r-h[u]; */
    /* 	if(bel[u]){ */
    /* 		to[u]=0; */
    /* 		boun[u]=d; */
    /* 	}else{ */
    /* 		to[u]=0; */
    /* 		boun[u]=d+1; */
    /* 		if(d==0){ */
    /* 			to[u]=-1; */
    /* 			boun[u]=0; */
    /* 		} */
    /* 	} */
    /* } */
    /* upmo(ans,-dp()); */

    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (bel[u]) {
        to[u] = 0;
        boun[u] = d + 1;
      } else {
        to[u] = 0;
        boun[u] = d;
      }
    }
    upmo(ans, dp());

    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (!bel[u]) {
        to[u] = 0;
        boun[u] = d;
      } else {
        to[u] = 0;
        boun[u] = d + 1;
        if (d == 0) {
          to[u] = 1;
          boun[u] = 0;
        }
      }
    }
    // upmo(ans,-dp());

    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (!bel[u]) {
        to[u] = 0;
        boun[u] = d;
      } else {
        to[u] = 0;
        boun[u] = d + 1;
        if (d == 0) {
          to[u] = -1;
          boun[u] = 0;
        }
      }
    }
    // upmo(ans,-dp());
    /* rep(u,1,n+1){ */
    /* 	int d; */
    /* 	if(!bel[u])d=r-1-h[u];else d=r-h[u]; */
    /* 	if(!bel[u]){ */
    /* 		to[u]=1; */
    /* 		boun[u]=d+1; */
    /* 		if(d==0){ */
    /* 			to[u]=0; */
    /* 			boun[u]=0; */
    /* 		} */
    /* 	}else{ */
    /* 		to[u]=0; */
    /* 		boun[u]=d+1; */
    /* 		if(d==0){ */
    /* 			to[u]=1; */
    /* 			boun[u]=0; */
    /* 		} */
    /* 	} */
    /* } */
    /* upmo(ans,dp()); */
    /* rep(u,1,n+1){ */
    /* 	int d; */
    /* 	if(!bel[u])d=r-1-h[u];else d=r-h[u]; */
    /* 	if(bel[u]){ */
    /* 		to[u]=1; */
    /* 		boun[u]=d+1; */
    /* 		if(d==0){ */
    /* 			to[u]=0; */
    /* 			boun[u]=0; */
    /* 		} */
    /* 	}else{ */
    /* 		to[u]=0; */
    /* 		boun[u]=d+1; */
    /* 		if(d==0){ */
    /* 			to[u]=1; */
    /* 			boun[u]=0; */
    /* 		} */
    /* 	} */
    /* } */
    /* upmo(ans,dp()); */
    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (!bel[u]) {
        to[u] = 0;
        boun[u] = d;
      } else {
        to[u] = 1;
        boun[u] = d;
      }
    }
    upmo(ans, -dp());
    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (bel[u]) {
        to[u] = 0;
        boun[u] = d;
      } else {
        to[u] = 1;
        boun[u] = d;
      }
    }
    upmo(ans, -dp());
  }

  printf("%d\\n", ans);
#ifdef JCVB
  debug("time: %d\\n", int(clock() - _time_jc));
#endif
  return 0;
}


Error: WA

Fixed submission:

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stdio.h>
#include <utility>
#include <vector>
using namespace std;
#define y0 y0z
#define y1 y1z
#define yn ynz
#define j0 j0z
#define j1 j1z
#define jn jnz
#define tm tmz
#define buli(x) (__builtin_popcountll(x))
#define bur0(x) (__builtin_ctzll(x))
#define bul2(x) (63 - __builtin_clzll(x))
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define fil(a, b) memset((a), (b), sizeof(a))
#define cl(a) fil(a, 0)
#define siz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define foreach(it, a)                                                         \\
  for (__typeof((a).begin()) it = (a).begin(); it != (a).end(); it++)
#define rep(i, a, b) for (int i = (a), _ed = (b); i < _ed; i++)
#define per(i, a, b) for (int i = (b)-1, _ed = (a); i >= _ed; i--)
#define forg(i, gu) for (int i = gu; ~i; i = e[i].next)
#define pw(x) ((ll(1)) << (x))
#define upmo(a, b) (((a) = ((a) + (b)) % mo) < 0 ? (a) += mo : (a))
#define mmo(a, b) (((a) = 1ll * (a) * (b) % mo) < 0 ? (a) += mo : (a))
void getre() {
  int x = 0;
  printf("%d\\n", 1 / x);
}
void gettle() {
  int res = 1;
  while (1)
    res <<= 1;
  printf("%d\\n", res);
}
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pii> vpii;
template <typename T, typename S> inline bool upmin(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T, typename S> inline bool upmax(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}
template <typename N, typename PN> inline N flo(N a, PN b) {
  return a >= 0 ? a / b : -((-a - 1) / b) - 1;
}
template <typename N, typename PN> inline N cei(N a, PN b) {
  return a > 0 ? (a - 1) / b + 1 : -(-a / b);
}
template <typename N> N gcd(N a, N b) { return b ? gcd(b, a % b) : a; }
template <typename N> inline int sgn(N a) {
  return a > 0 ? 1 : (a < 0 ? -1 : 0);
}
#if ((_WIN32 || __WIN32__) && __cplusplus < 201103L)
#define lld "%I64d"
#else
#define lld "%lld"
#endif
inline void gn(long long &x) {
  int sg = 1;
  char c;
  while (((c = getchar()) < '0' || c > '9') && c != '-')
    ;
  c == '-' ? (sg = -1, x = 0) : (x = c - '0');
  while ((c = getchar()) >= '0' && c <= '9')
    x = x * 10 + c - '0';
  x *= sg;
}
inline void gn(int &x) {
  long long t;
  gn(t);
  x = t;
}
inline void gn(unsigned long long &x) {
  long long t;
  gn(t);
  x = t;
}
inline void gn(double &x) {
  double t;
  scanf("%lf", &t);
  x = t;
}
inline void gn(long double &x) {
  double t;
  scanf("%lf", &t);
  x = t;
}
inline void gs(char *s) { scanf("%s", s); }
inline void gc(char &c) {
  while ((c = getchar()) > 126 || c < 33)
    ;
}
inline void pc(char c) { putchar(c); }
#ifdef JCVB
#define debug(...) fprintf(stderr, __VA_ARGS__)
#else
#define debug(...)
#endif
typedef long long ll;
typedef double db;
inline ll sqr(ll a) { return a * a; }
inline db sqrf(db a) { return a * a; }
const int inf = 0x3f3f3f3f;
// const ll inf=0x3f3f3f3f3f3f3f3fll;
const db pi = 3.14159265358979323846264338327950288L;
const db eps = 1e-6;
const int mo = 1e9 + 7;
// int qp(int a,ll b){int
// n=1;do{if(b&1)n=1ll*n*a%mo;a=1ll*a*a%mo;}while(b>>=1);return n;}

const int TREE_MAXV = 3000 + 5;
struct edge {
  int v, next;
} e[TREE_MAXV * 2];
int g[TREE_MAXV], etot;
int qu[TREE_MAXV], pre[TREE_MAXV];
int h[33333];
int n;
void ae(int u, int v) {
  e[etot].v = v;
  e[etot].next = g[u];
  g[u] = etot++;
}

int bel[33333];
void bfs(int rt) {
  int p = 0, q = 0;
  pre[rt] = 0;
  h[rt] = 0;
  qu[q++] = rt;
  while (p != q) {
    int u = qu[p++];
    for (int i = g[u]; ~i; i = e[i].next)
      if (e[i].v != pre[u]) {
        pre[e[i].v] = u;
        bel[e[i].v] |= bel[u];
        h[e[i].v] = h[u] + 1;
        qu[q++] = e[i].v;
      }
  }
}
void tree_init() {
  static bool ini = 0;
  if (!ini) {
    ini = 1;
    memset(g, -1, sizeof(g));
  } else {
    for (int i = 0; i <= n; i++)
      g[i] = -1;
  }
  etot = 0;
}
void readedge() {
  for (int i = 1; i < n; i++) {
    int x, y;
    gn(x);
    gn(y);
    ae(x, y);
    ae(y, x);
  }
}

int boun[2222], to[2222];
const int zer = 1111;
int f[1111][2222];

int dp() {
  cl(f);
  for (int i = n - 1; i >= 0; i--) {
    int u = qu[i];

    for (int j = to[u] - boun[u]; j <= to[u] + boun[u]; j++) {
      f[u][j + zer] = 1;
      forg(t, g[u]) if (e[t].v != pre[u])
          mmo(f[u][j + zer], (f[e[t].v][j - 1 + zer] + f[e[t].v][j + 1 + zer]));
    }
  }
  int ret = 0;
  rep(t, 0, 2222) upmo(ret, f[qu[0]][t]);
  return ret;
}

int main() {
#ifdef JCVB
  // freopen("1.in","r",stdin);
  // freopen("1.out","w",stdout);
  int _time_jc = clock();
#endif
  gn(n);
  tree_init();
  readedge();

  static int dis1[2222];

  bfs(1);
  int ma = 1;
  rep(u, 2, n + 1) if (h[u] > h[ma]) ma = u;
  bfs(ma);
  int mav = 1;
  rep(u, 1, n + 1) if (h[u] > h[mav]) mav = u;

  bfs(mav);
  rep(i, 1, n + 1) dis1[i] = h[i];
  bfs(ma);
  int r;

  r = cei(h[mav], 2);
  int rt = 0, rt2 = 0;

  if (h[mav] % 2 == 0) {
    rep(i, 1, n + 1) {
      if (dis1[i] == h[i] && h[i] == h[mav] / 2)
        rt = i;
    }
  } else {
    rep(i, 1, n + 1) {
      if (dis1[i] == h[mav] / 2 && h[i] == (h[mav] + 1) / 2)
        rt = i;
      if (dis1[i] == (h[mav] + 1) / 2 && h[i] == (h[mav] + 0) / 2)
        rt2 = i;
    }
  }

  bel[rt2] = 1;
  bfs(rt);

  int ans = 0;
  if (rt2 == 0) {
    getre();
    rep(u, 1, n + 1) boun[u] = r - h[u], to[u] = 0;
    upmo(ans, dp());
  } else {
    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (bel[u]) {
        to[u] = 0;
        boun[u] = d;
      } else {
        to[u] = 0;
        boun[u] = d + 1;
      }
    }
    upmo(ans, dp());
    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (bel[u]) {
        to[u] = 0;
        boun[u] = d;
      } else {
        to[u] = 0;
        boun[u] = d + 1;
        if (d == 0) {
          to[u] = 1;
          boun[u] = 0;
        }
      }
    }
    upmo(ans, -dp());

    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (bel[u]) {
        to[u] = 0;
        boun[u] = d;
      } else {
        to[u] = 0;
        boun[u] = d + 1;
        if (d == 0) {
          to[u] = -1;
          boun[u] = 0;
        }
      }
    }
    upmo(ans, -dp());

    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (bel[u]) {
        to[u] = 0;
        boun[u] = d + 1;
      } else {
        to[u] = 0;
        boun[u] = d;
      }
    }
    upmo(ans, dp());

    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (!bel[u]) {
        to[u] = 0;
        boun[u] = d;
      } else {
        to[u] = 0;
        boun[u] = d + 1;
        if (d == 0) {
          to[u] = 1;
          boun[u] = 0;
        }
      }
    }
    upmo(ans, -dp());

    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (!bel[u]) {
        to[u] = 0;
        boun[u] = d;
      } else {
        to[u] = 0;
        boun[u] = d + 1;
        if (d == 0) {
          to[u] = -1;
          boun[u] = 0;
        }
      }
    }
    upmo(ans, -dp());
    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (!bel[u]) {
        to[u] = 1;
        boun[u] = d + 1;
        if (d == 0) {
          to[u] = 0;
          boun[u] = 0;
        }
      } else {
        to[u] = 0;
        boun[u] = d + 1;
        if (d == 0) {
          to[u] = 1;
          boun[u] = 0;
        }
      }
    }
    upmo(ans, dp());
    rep(u, 1, n + 1) {
      int d;
      if (!bel[u])
        d = r - 1 - h[u];
      else
        d = r - h[u];
      if (bel[u]) {
        to[u] = 1;
        boun[u] = d + 1;
        if (d == 0) {
          to[u] = 0;
          boun[u] = 0;
        }
      } else {
        to[u] = 0;
        boun[u] = d + 1;
        if (d == 0) {
          to[u] = 1;
          boun[u] = 0;
        }
      }
    }
    upmo(ans, dp());
  }

  printf("%d\\n", ans);
#ifdef JCVB
  debug("time: %d\\n", int(clock() - _time_jc));
#endif
  return 0;
}