Problem p03175 (C++)

Buggy submission (status: Runtime Error):
#include "bits/stdc++.h"

using namespace std;

#define FI freopen("in.txt", "r", stdin)
#define FO freopen("out.txt", "w", stdout)
#define FAST ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL)

#define FOR(i, n) for (int i = 1; i <= n; i++)
#define For(i, n) for (int i = 0; i < n; i++)
#define ROF(i, n) for (int i = n; i >= 1; i--)
#define Rof(i, n) for (int i = n - 1; i >= 0; i--)
#define FORI(i, n) for (auto i : n)

#define ll long long
#define ull unsigned long long
#define vi vector<int>
#define vl vector<ll>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define mk make_pair
#define ff first
#define ss second
#define eb emplace_back
#define em emplace
#define pb push_back
#define ppb pop_back
#define All(a) a.begin(), a.end()
#define memo(a, b) memset(a, b, sizeof a)
#define Sort(a) sort(All(a))
#define ED(a) Sort(a), a.erase(unique(All(a)), a.end())
#define rev(a) reverse(All(a))
#define sz(a) (int)a.size()
#define max3(a, b, c) max(a, max(b, c))
#define min3(a, b, c) min(a, min(b, c))
#define maxAll(a) *max_element(All(a))
#define minAll(a) *min_element(All(a))
#define allUpper(a) transform(All(a), a.begin(), ::toupper)
#define allLower(a) transform(All(a), a.begin(), ::tolower)
#define endl '\n'
#define nl puts("")
#define ub upper_bound
#define lb lower_bound
#define Exp exp(1.0)
#define PIE 2 * acos(0.0)
#define Sin(a) sin(((a)*PIE) / 180.0)
#define EPS 1e-9

#include "ext/pb_ds/assoc_container.hpp"
#include "ext/pb_ds/tree_policy.hpp"
using namespace __gnu_pbds;

template <typename T>
using orderset =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

#include "ext/rope"
using namespace __gnu_cxx;

// rope <int> Rope;

// int dr[] = {1, -1, 0, 0}; // 4 Direction
// int dc[] = {0, 0, 1, -1};
// int dr[] = {0, 0, 1, -1, 1, 1, -1, -1}; // 8 Direction
// int dc[] = {1, -1, 0, 0, 1, -1, 1, -1};
// int dr[] = {-1, 1, -2, -2, -1, 1, 2, 2}; // knight Moves
// int dc[] = {-2, -2, -1, 1, 2, 2, 1, -1};

#define trace1(x) cerr << #x << ": " << x << endl;
#define trace2(x, y)                                                           \
  cerr << #x << ": " << x << " | " << #y << ": " << y << endl;
#define trace3(x, y, z)                                                        \
  cerr << #x << ": " << x << " | " << #y << ": " << y << " | " << #z << ": "   \
       << z << endl;
#define trace4(a, b, c, d)                                                     \
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << endl;
#define trace5(a, b, c, d, e)                                                  \
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << " | " << #e << ": " << e << endl;
#define trace6(a, b, c, d, e, f)                                               \
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << " | " << #e << ": " << e << " | "   \
       << #f << ": " << f << endl;

inline int setbit(int mask, int pos) { return mask |= (1 << pos); }
inline int resetbit(int mask, int pos) { return mask &= ~(1 << pos); }
inline int togglebit(int mask, int pos) { return mask ^= (1 << pos); }
inline bool checkbit(int mask, int pos) { return (bool)(mask & (1 << pos)); }

#define popcount(mask) __builtin_popcount(mask)     // count set bit
#define popcountLL(mask) __builtin_popcountll(mask) // for long long

inline int read() {
  int a;
  scanf("%d", &a);
  return a;
}
inline ll readLL() {
  ll a;
  scanf("%lld", &a);
  return a;
}
inline double readDD() {
  double a;
  scanf("%lf", &a);
  return a;
}

template <typename T> string toString(T num) {
  stringstream ss;
  ss << num;
  return ss.str();
}
int toInt(string s) {
  int num;
  istringstream iss(s);
  iss >> num;
  return num;
}
ll toLLong(string s) {
  ll num;
  istringstream iss(s);
  iss >> num;
  return num;
}

#define inf 1e17
#define mod 1000000007

static const int maxn = 1e2 + 5;
static const int logn = 18;

vector<int> graph[maxn];

int tnode;
int tlebel;
int lastNode;

inline void dfs(int u = 1, int p = -1, int lebel = 1) {
  if (lebel > tlebel)
    tlebel = lebel;
  lastNode = u;
  for (int v : graph[u]) {
    if (v == p)
      continue;
    dfs(v, u, lebel + 1);
  }
}

ll dp[maxn][2];
bool memoize[maxn][2];

inline ll ways(int u, int p, int color) {
  if (sz(graph[u]) == 1 && p)
    return 1;
  ll &ret = dp[u][color];
  bool &mem = memoize[u][color];
  if (mem)
    return ret;
  mem = 1;
  ll mul = 1;
  for (int v : graph[u]) {
    if (v == p)
      continue;
    ll sum = 0;
    if (color == 0) {
      sum = (sum + ways(v, u, color)) % mod;
      sum = (sum + ways(v, u, color ^ 1)) % mod;
    } else {
      sum = (sum + ways(v, u, color ^ 1)) % mod;
    }
    mul = (mul * sum) % mod;
  }
  return ret = mul;
}

int main() {
  // FI;
  tnode = read();
  FOR(i, tnode - 1) {
    int u = read();
    int v = read();
    graph[u].eb(v);
    graph[v].eb(u);
  }
  dfs();
  trace1(tlebel);
  ll tways = (ways(1, 0, 0) + ways(1, 0, 1)) % mod;
  printf("%lld", tways);
}


Fixed submission:
#include "bits/stdc++.h"

using namespace std;

#define FI freopen("in.txt", "r", stdin)
#define FO freopen("out.txt", "w", stdout)
#define FAST ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL)

#define FOR(i, n) for (int i = 1; i <= n; i++)
#define For(i, n) for (int i = 0; i < n; i++)
#define ROF(i, n) for (int i = n; i >= 1; i--)
#define Rof(i, n) for (int i = n - 1; i >= 0; i--)
#define FORI(i, n) for (auto i : n)

#define ll long long
#define ull unsigned long long
#define vi vector<int>
#define vl vector<ll>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define mk make_pair
#define ff first
#define ss second
#define eb emplace_back
#define em emplace
#define pb push_back
#define ppb pop_back
#define All(a) a.begin(), a.end()
#define memo(a, b) memset(a, b, sizeof a)
#define Sort(a) sort(All(a))
#define ED(a) Sort(a), a.erase(unique(All(a)), a.end())
#define rev(a) reverse(All(a))
#define sz(a) (int)a.size()
#define max3(a, b, c) max(a, max(b, c))
#define min3(a, b, c) min(a, min(b, c))
#define maxAll(a) *max_element(All(a))
#define minAll(a) *min_element(All(a))
#define allUpper(a) transform(All(a), a.begin(), ::toupper)
#define allLower(a) transform(All(a), a.begin(), ::tolower)
#define endl '\n'
#define nl puts("")
#define ub upper_bound
#define lb lower_bound
#define Exp exp(1.0)
#define PIE 2 * acos(0.0)
#define Sin(a) sin(((a)*PIE) / 180.0)
#define EPS 1e-9

#include "ext/pb_ds/assoc_container.hpp"
#include "ext/pb_ds/tree_policy.hpp"
using namespace __gnu_pbds;

template <typename T>
using orderset =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

#include "ext/rope"
using namespace __gnu_cxx;

// rope <int> Rope;

// int dr[] = {1, -1, 0, 0}; // 4 Direction
// int dc[] = {0, 0, 1, -1};
// int dr[] = {0, 0, 1, -1, 1, 1, -1, -1}; // 8 Direction
// int dc[] = {1, -1, 0, 0, 1, -1, 1, -1};
// int dr[] = {-1, 1, -2, -2, -1, 1, 2, 2}; // knight Moves
// int dc[] = {-2, -2, -1, 1, 2, 2, 1, -1};

#define trace1(x) cerr << #x << ": " << x << endl;
#define trace2(x, y)                                                           \
  cerr << #x << ": " << x << " | " << #y << ": " << y << endl;
#define trace3(x, y, z)                                                        \
  cerr << #x << ": " << x << " | " << #y << ": " << y << " | " << #z << ": "   \
       << z << endl;
#define trace4(a, b, c, d)                                                     \
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << endl;
#define trace5(a, b, c, d, e)                                                  \
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << " | " << #e << ": " << e << endl;
#define trace6(a, b, c, d, e, f)                                               \
  cerr << #a << ": " << a << " | " << #b << ": " << b << " | " << #c << ": "   \
       << c << " | " << #d << ": " << d << " | " << #e << ": " << e << " | "   \
       << #f << ": " << f << endl;

inline int setbit(int mask, int pos) { return mask |= (1 << pos); }
inline int resetbit(int mask, int pos) { return mask &= ~(1 << pos); }
inline int togglebit(int mask, int pos) { return mask ^= (1 << pos); }
inline bool checkbit(int mask, int pos) { return (bool)(mask & (1 << pos)); }

#define popcount(mask) __builtin_popcount(mask)     // count set bit
#define popcountLL(mask) __builtin_popcountll(mask) // for long long

inline int read() {
  int a;
  scanf("%d", &a);
  return a;
}
inline ll readLL() {
  ll a;
  scanf("%lld", &a);
  return a;
}
inline double readDD() {
  double a;
  scanf("%lf", &a);
  return a;
}

template <typename T> string toString(T num) {
  stringstream ss;
  ss << num;
  return ss.str();
}
int toInt(string s) {
  int num;
  istringstream iss(s);
  iss >> num;
  return num;
}
ll toLLong(string s) {
  ll num;
  istringstream iss(s);
  iss >> num;
  return num;
}

#define inf 1e17
#define mod 1000000007

static const int maxn = 1e5 + 5;
static const int logn = 18;

vector<int> graph[maxn];

int tnode;
int tlebel;
int lastNode;

inline void dfs(int u = 1, int p = -1, int lebel = 1) {
  if (lebel > tlebel)
    tlebel = lebel;
  lastNode = u;
  for (int v : graph[u]) {
    if (v == p)
      continue;
    dfs(v, u, lebel + 1);
  }
}

ll dp[maxn][2];
bool memoize[maxn][2];

inline ll ways(int u, int p, int color) {
  if (sz(graph[u]) == 1 && p)
    return 1;
  ll &ret = dp[u][color];
  bool &mem = memoize[u][color];
  if (mem)
    return ret;
  mem = 1;
  ll mul = 1;
  for (int v : graph[u]) {
    if (v == p)
      continue;
    ll sum = 0;
    if (color == 0) {
      sum = (sum + ways(v, u, color)) % mod;
      sum = (sum + ways(v, u, color ^ 1)) % mod;
    } else {
      sum = (sum + ways(v, u, color ^ 1)) % mod;
    }
    mul = (mul * sum) % mod;
  }
  return ret = mul;
}

int main() {
  // FI;
  tnode = read();
  FOR(i, tnode - 1) {
    int u = read();
    int v = read();
    graph[u].eb(v);
    graph[v].eb(u);
  }
  dfs();
  trace1(tlebel);
  ll tways = (ways(1, 0, 0) + ways(1, 0, 1)) % mod;
  printf("%lld", tways);
}