Problem p03513 (C++)

Buggy submission (status: Time Limit Exceeded):
// #pragma GCC target("avx")  // CPU 処理並列化
// #pragma GCC optimize("O3")  // CPU 処理並列化
// #pragma GCC optimize("unroll-loops")  // 条件処理の呼び出しを減らす
// #define BEGIN_STACK_EXTEND(size) void * stack_extend_memory_ =
// malloc(size);void * stack_extend_origin_memory_;char *
// stack_extend_dummy_memory_ = (char*)alloca((1+(int)(((long
// long)stack_extend_memory_)&127))*16);*stack_extend_dummy_memory_ = 0;asm
// volatile("mov %%rsp, %%rbx\nmov %%rax,
// %%rsp":"=b"(stack_extend_origin_memory_):"a"((char*)stack_extend_memory_+(size)-1024));
// #define END_STACK_EXTEND asm volatile("mov %%rax,
// %%rsp"::"a"(stack_extend_origin_memory_));free(stack_extend_memory_);

#include <algorithm>
#include <bitset>
#include <cassert>
#include <complex>
#include <deque>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <time.h>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;
const long long mod = 1000000007;
const long long inf = mod * mod;
const long long d2 = (mod + 1) / 2;
const double EPS = 1e-11;
const double INF = 1e+10;
const double PI = acos(-1.0);
const int C_SIZE = 11100000;
const int UF_SIZE = 3100000;
namespace {
long long fact[C_SIZE];
long long finv[C_SIZE];
long long inv[C_SIZE];
inline long long Comb(int a, int b) {
  if (a < b || b < 0)
    return 0;
  return fact[a] * finv[b] % mod * finv[a - b] % mod;
}
void init_C(int n) {
  fact[0] = finv[0] = inv[1] = 1;
  for (int i = 2; i < n; i++) {
    inv[i] = (mod - (mod / i) * inv[mod % i] % mod) % mod;
  }
  for (int i = 1; i < n; i++) {
    fact[i] = fact[i - 1] * i % mod;
    finv[i] = finv[i - 1] * inv[i] % mod;
  }
}
long long pw(long long a, long long b) {
  if (a < 0LL)
    return 0;
  if (b < 0LL)
    return 0;
  long long ret = 1;
  while (b) {
    if (b % 2)
      ret = ret * a % mod;
    a = a * a % mod;
    b /= 2;
  }
  return ret;
}
long long pw_mod(long long a, long long b, long long M) {
  if (a < 0LL)
    return 0;
  if (b < 0LL)
    return 0;
  long long ret = 1;
  while (b) {
    if (b % 2)
      ret = ret * a % M;
    a = a * a % M;
    b /= 2;
  }
  return ret;
}
int pw_mod_int(int a, int b, int M) {
  if (a < 0)
    return 0;
  if (b < 0)
    return 0;
  int ret = 1;
  while (b) {
    if (b % 2)
      ret = (long long)ret * a % M;
    a = (long long)a * a % M;
    b /= 2;
  }
  return ret;
}
int ABS(int a) { return max(a, -a); }
long long ABS(long long a) { return max(a, -a); }
double ABS(double a) { return max(a, -a); }
int sig(double r) { return (r < -EPS) ? -1 : (r > +EPS) ? +1 : 0; }
int UF[UF_SIZE];
void init_UF(int n) {
  for (int i = 0; i < n; i++)
    UF[i] = -1;
}
int FIND(int a) {
  if (UF[a] < 0)
    return a;
  return UF[a] = FIND(UF[a]);
}
void UNION(int a, int b) {
  a = FIND(a);
  b = FIND(b);
  if (a == b)
    return;
  if (UF[a] > UF[b])
    swap(a, b);
  UF[a] += UF[b];
  UF[b] = a;
}
} // namespace
// ここから編集しろ
long long dp[1 << 15];
int p3[16];
int n;
int g[20][20];
int C[16][1 << 15];
long long calc(int a) {
  if (~dp[a])
    return dp[a];
  long long ret = 1;
  int t = 0;
  if (!(a & 1))
    t = 1;
  int tmp = a;
  while (tmp) {
    if (tmp != a && (tmp & (1 << t))) {
      int cnt = 0;
      for (int i = 0; i < n; i++) {
        if (!(tmp & (1 << i)))
          continue;
        cnt += C[i][a - tmp];
      }
      ret = (ret + mod - calc(tmp) * pw(d2, cnt) % mod) % mod;
    }
    tmp = (tmp - 1) & a;
  }
  // printf("%d: %lld\n",a,ret);
  return dp[a] = ret;
}
int main() {
  int a, b;
  scanf("%d%d", &a, &b);
  n = a;
  for (int i = 0; i < b; i++) {
    int s, t;
    scanf("%d%d", &s, &t);
    s--;
    t--;
    g[s][t] = g[t][s] = 1;
  }
  for (int i = 0; i < a; i++) {
    for (int j = 0; j < (1 << a); j++) {
      for (int k = 0; k < a; k++) {
        if (j & (1 << k)) {
          if (g[i][k])
            C[i][j]++;
        }
      }
    }
  }
  long long ret = 0;
  p3[0] = 1;
  for (int i = 0; i < (1 << a); i++)
    dp[i] = -1;
  for (int i = 1; i < 16; i++)
    p3[i] = p3[i - 1] * 3;
  for (int i = 0; i < p3[a]; i++) {
    int A = 0;
    int B = 0;
    for (int j = 0; j < a; j++) {
      if (i / p3[j] % 3 == 1)
        A += (1 << j);
      if (i / p3[j] % 3 == 2)
        B += (1 << j);
    }
    if (!(A & 1))
      continue;
    if (!(B & 2))
      continue;
    bool ok = true;
    int cnt = 0;
    for (int j = 0; j < a; j++) {
      if (!(A & (1 << j)))
        continue;
      if (C[j][B])
        ok = false;
    }
    if (!ok)
      continue;
    for (int j = 0; j < a; j++) {
      if (!(A & (1 << j)))
        continue;
      cnt += C[j][(1 << a) - 1 - A];
    }
    for (int j = 0; j < a; j++) {
      if (!(B & (1 << j)))
        continue;
      cnt += C[j][(1 << a) - 1 - B];
    }
    // printf("%d: %lld\n",i,pw(d2,cnt)*calc(A)%mod*calc(B)%mod);
    ret = (ret + pw(d2, cnt) * calc(A) % mod * calc(B)) % mod;
  }
  ret = (1 + mod - ret) % mod;
  ret = ret * pw(2, b) % mod;
  printf("%lld\n", ret);
}

Fixed submission:
#pragma GCC target("avx")            // CPU 処理並列化
#pragma GCC optimize("O3")           // CPU 処理並列化
#pragma GCC optimize("unroll-loops") // 条件処理の呼び出しを減らす
// #define BEGIN_STACK_EXTEND(size) void * stack_extend_memory_ =
// malloc(size);void * stack_extend_origin_memory_;char *
// stack_extend_dummy_memory_ = (char*)alloca((1+(int)(((long
// long)stack_extend_memory_)&127))*16);*stack_extend_dummy_memory_ = 0;asm
// volatile("mov %%rsp, %%rbx\nmov %%rax,
// %%rsp":"=b"(stack_extend_origin_memory_):"a"((char*)stack_extend_memory_+(size)-1024));
// #define END_STACK_EXTEND asm volatile("mov %%rax,
// %%rsp"::"a"(stack_extend_origin_memory_));free(stack_extend_memory_);

#include <algorithm>
#include <bitset>
#include <cassert>
#include <complex>
#include <deque>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <time.h>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;
const long long mod = 1000000007;
const long long inf = mod * mod;
const long long d2 = (mod + 1) / 2;
const double EPS = 1e-11;
const double INF = 1e+10;
const double PI = acos(-1.0);
const int C_SIZE = 11100000;
const int UF_SIZE = 3100000;
namespace {
long long fact[C_SIZE];
long long finv[C_SIZE];
long long inv[C_SIZE];
inline long long Comb(int a, int b) {
  if (a < b || b < 0)
    return 0;
  return fact[a] * finv[b] % mod * finv[a - b] % mod;
}
void init_C(int n) {
  fact[0] = finv[0] = inv[1] = 1;
  for (int i = 2; i < n; i++) {
    inv[i] = (mod - (mod / i) * inv[mod % i] % mod) % mod;
  }
  for (int i = 1; i < n; i++) {
    fact[i] = fact[i - 1] * i % mod;
    finv[i] = finv[i - 1] * inv[i] % mod;
  }
}
long long pw(long long a, long long b) {
  if (a < 0LL)
    return 0;
  if (b < 0LL)
    return 0;
  long long ret = 1;
  while (b) {
    if (b % 2)
      ret = ret * a % mod;
    a = a * a % mod;
    b /= 2;
  }
  return ret;
}
long long pw_mod(long long a, long long b, long long M) {
  if (a < 0LL)
    return 0;
  if (b < 0LL)
    return 0;
  long long ret = 1;
  while (b) {
    if (b % 2)
      ret = ret * a % M;
    a = a * a % M;
    b /= 2;
  }
  return ret;
}
int pw_mod_int(int a, int b, int M) {
  if (a < 0)
    return 0;
  if (b < 0)
    return 0;
  int ret = 1;
  while (b) {
    if (b % 2)
      ret = (long long)ret * a % M;
    a = (long long)a * a % M;
    b /= 2;
  }
  return ret;
}
int ABS(int a) { return max(a, -a); }
long long ABS(long long a) { return max(a, -a); }
double ABS(double a) { return max(a, -a); }
int sig(double r) { return (r < -EPS) ? -1 : (r > +EPS) ? +1 : 0; }
int UF[UF_SIZE];
void init_UF(int n) {
  for (int i = 0; i < n; i++)
    UF[i] = -1;
}
int FIND(int a) {
  if (UF[a] < 0)
    return a;
  return UF[a] = FIND(UF[a]);
}
void UNION(int a, int b) {
  a = FIND(a);
  b = FIND(b);
  if (a == b)
    return;
  if (UF[a] > UF[b])
    swap(a, b);
  UF[a] += UF[b];
  UF[b] = a;
}
} // namespace
// ここから編集しろ
long long dp[1 << 15];
int p3[16];
int n;
int g[20][20];
int C[16][1 << 15];
long long calc(int a) {
  if (~dp[a])
    return dp[a];
  long long ret = 1;
  int t = 0;
  if (!(a & 1))
    t = 1;
  int tmp = a;
  while (tmp) {
    if (tmp != a && (tmp & (1 << t))) {
      int cnt = 0;
      for (int i = 0; i < n; i++) {
        if (!(tmp & (1 << i)))
          continue;
        cnt += C[i][a - tmp];
      }
      ret = (ret + mod - calc(tmp) * pw(d2, cnt) % mod) % mod;
    }
    tmp = (tmp - 1) & a;
  }
  // printf("%d: %lld\n",a,ret);
  return dp[a] = ret;
}
int main() {
  int a, b;
  scanf("%d%d", &a, &b);
  n = a;
  for (int i = 0; i < b; i++) {
    int s, t;
    scanf("%d%d", &s, &t);
    s--;
    t--;
    g[s][t] = g[t][s] = 1;
  }
  for (int i = 0; i < a; i++) {
    for (int j = 0; j < (1 << a); j++) {
      for (int k = 0; k < a; k++) {
        if (j & (1 << k)) {
          if (g[i][k])
            C[i][j]++;
        }
      }
    }
  }
  long long ret = 0;
  p3[0] = 1;
  for (int i = 0; i < (1 << a); i++)
    dp[i] = -1;
  for (int i = 1; i < 16; i++)
    p3[i] = p3[i - 1] * 3;
  for (int i = 0; i < p3[a]; i++) {
    int A = 0;
    int B = 0;
    for (int j = 0; j < a; j++) {
      if (i / p3[j] % 3 == 1)
        A += (1 << j);
      if (i / p3[j] % 3 == 2)
        B += (1 << j);
    }
    if (!(A & 1))
      continue;
    if (!(B & 2))
      continue;
    bool ok = true;
    int cnt = 0;
    for (int j = 0; j < a; j++) {
      if (!(A & (1 << j)))
        continue;
      if (C[j][B])
        ok = false;
    }
    if (!ok)
      continue;
    for (int j = 0; j < a; j++) {
      if (!(A & (1 << j)))
        continue;
      cnt += C[j][(1 << a) - 1 - A];
    }
    for (int j = 0; j < a; j++) {
      if (!(B & (1 << j)))
        continue;
      cnt += C[j][(1 << a) - 1 - B];
    }
    // printf("%d: %lld\n",i,pw(d2,cnt)*calc(A)%mod*calc(B)%mod);
    ret = (ret + pw(d2, cnt) * calc(A) % mod * calc(B)) % mod;
  }
  ret = (1 + mod - ret) % mod;
  ret = ret * pw(2, b) % mod;
  printf("%lld\n", ret);
}