Problem p00831 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))

// #define DEBUG

#ifdef DEBUG
#define dump(...) fprintf(stderr, __VA_ARGS__)
#else
#define dump(...)
#endif

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

const double EPS = 1e-10;
const double PI = acos(-1.0);
const ll inf = 1LL << 62;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0)
    g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}

random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);

const int N = 1e6;
vi graph[N];

using ResElem = tuple<string, string>;
set<ResElem> s;

inline void add_edge(int a, int b) {
  graph[a].emplace_back(b);
  graph[b].emplace_back(a);
}

int d, n;
map<string, int> s2i;
map<int, string> i2s;

void dfs(int sv, int v, int depth) {
  if (depth > d)
    return;
  if (sv != v and v < n) {
    string a = i2s[v], b = i2s[sv];
    if (a > b)
      swap(a, b);
    s.insert(ResElem(a, b));
  }

  for (auto &nv : graph[v]) {
    dfs(sv, nv, depth + 1);
  }
}

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  for (; cin >> n >> d, n;) {
    vector<string> names(n);
    for (auto &e : names)
      cin >> e;

    s2i.clear();
    i2s.clear();
    int idx = 0;
    auto add_vertex = [&](string &name) {
      if (s2i.find(name) == end(s2i)) {
        s2i[name] = idx;
        i2s[idx] = name;
        idx++;
      }
      return s2i[name];
    };
    for (auto &e : names)
      add_vertex(e);

    rep(i, N) graph[i].clear();
    for (auto &cur : names) {
      string next;
      int len = cur.size();
      int v = s2i[cur];

      // delete
      rep(i, len) {
        next = cur.substr(0, i) + cur.substr(i + 1);
        int nv = add_vertex(next);
        add_edge(v, nv);
      }

      // insert
      rep(i, len + 1) {
        rep(j, 'z' - 'a' + 1) {
          char c = (char)('a' + j);
          next = cur.substr(0, i) + c + cur.substr(i);
          int nv = add_vertex(next);
          add_edge(v, nv);
        }
      }

      // replace
      rep(i, len) {
        rep(j, 'z' - 'a' + 1) {
          char c = (char)('a' + j);
          next = cur.substr(0, i) + c;
          if (i + 1 < len)
            next += cur.substr(i + 1);
          int nv = add_vertex(next);
          add_edge(v, nv);
        }
      }

      // swap
      rep(i, len - 1) {
        next = cur;
        swap(next[i], next[i + 1]);
        int nv = add_vertex(next);
        add_edge(v, nv);
      }
    }

    s.clear();
    rep(i, n) { dfs(i, i, 0); }

    for (auto &e : s) {
      string a, b;
      tie(a, b) = e;
      cout << a << "," << b << endl;
    }
    cout << s.size() << endl;
  }

  return 0;
}

Error: WA

Fixed submission:

#include <bits/stdc++.h>

#define _overload(_1, _2, _3, name, ...) name
#define _rep(i, n) _range(i, 0, n)
#define _range(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rep(...) _overload(__VA_ARGS__, _range, _rep, )(__VA_ARGS__)

#define _rrep(i, n) _rrange(i, n, 0)
#define _rrange(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rrep(...) _overload(__VA_ARGS__, _rrange, _rrep, )(__VA_ARGS__)

#define _all(arg) begin(arg), end(arg)
#define uniq(arg) sort(_all(arg)), (arg).erase(unique(_all(arg)), end(arg))
#define getidx(ary, key) lower_bound(_all(ary), key) - begin(ary)
#define clr(a, b) memset((a), (b), sizeof(a))
#define bit(n) (1LL << (n))

// #define DEBUG

#ifdef DEBUG
#define dump(...) fprintf(stderr, __VA_ARGS__)
#else
#define dump(...)
#endif

template <class T> bool chmax(T &a, const T &b) {
  return (a < b) ? (a = b, 1) : 0;
}
template <class T> bool chmin(T &a, const T &b) {
  return (b < a) ? (a = b, 1) : 0;
}

using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

const double EPS = 1e-10;
const double PI = acos(-1.0);
const ll inf = 1LL << 62;
const ll mod = 1000000007LL;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

ll extgcd(ll a, ll b, ll &x, ll &y) {
  x = 1, y = 0;
  ll g = a;
  if (b != 0)
    g = extgcd(b, a % b, y, x), y -= a / b * x;
  return g;
}
ll ADD(const ll &a, const ll &b, const ll &mod) { return (a + b) % mod; }
ll SUB(const ll &a, const ll &b, const ll &mod) { return (a - b + mod) % mod; }
ll MUL(const ll &a, const ll &b, const ll &mod) { return (1LL * a * b) % mod; }
ll DIV(const ll &a, const ll &b, const ll &mod) {
  ll x, y;
  extgcd(b, mod, x, y);
  return MUL(a, (x + mod) % mod, mod);
}

random_device rd;
mt19937 mt(rd());
uniform_int_distribution<int> dice(1, 6);
uniform_real_distribution<double> score(0.0, 10.0);

const int N = 1e5;
vi graph[N];

using ResElem = tuple<int, int>;
set<ResElem> s;

inline void add_edge(int a, int b) {
  graph[a].emplace_back(b);
  graph[b].emplace_back(a);
}

int d, n;
map<string, int> s2i;
map<int, string> i2s;

void dfs(int sv, int v, int depth) {
  if (depth > d)
    return;
  if (sv != v and v < n) {
    string a = i2s[v], b = i2s[sv];
    if (a > b)
      swap(a, b);
    s.insert(ResElem(s2i[a], s2i[b]));
  }

  for (auto &nv : graph[v]) {
    dfs(sv, nv, depth + 1);
  }
}

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  for (; cin >> n >> d, n;) {
    vector<string> names(n);
    for (auto &e : names)
      cin >> e;

    s2i.clear();
    i2s.clear();
    int idx = 0;
    auto add_vertex = [&](string &name) {
      if (s2i.find(name) == end(s2i)) {
        s2i[name] = idx;
        i2s[idx] = name;
        idx++;
      }
      return s2i[name];
    };
    for (auto &e : names)
      add_vertex(e);

    rep(i, N) graph[i].clear();
    for (auto &cur : names) {
      string next;
      int len = cur.size();
      int v = s2i[cur];

      // delete
      rep(i, len) {
        next = cur.substr(0, i) + cur.substr(i + 1);
        int nv = add_vertex(next);
        add_edge(v, nv);
      }

      // insert
      rep(i, len + 1) {
        rep(j, 'z' - 'a' + 1) {
          char c = (char)('a' + j);
          next = cur.substr(0, i) + c + cur.substr(i);
          int nv = add_vertex(next);
          add_edge(v, nv);
        }
      }

      // replace
      rep(i, len) {
        rep(j, 'z' - 'a' + 1) {
          char c = (char)('a' + j);
          next = cur.substr(0, i) + c + cur.substr(i + 1);
          int nv = add_vertex(next);
          add_edge(v, nv);
        }
      }

      // swap
      rep(i, len - 1) {
        next = cur;
        swap(next[i], next[i + 1]);
        int nv = add_vertex(next);
        add_edge(v, nv);
      }
    }

    s.clear();
    rep(i, n) { dfs(i, i, 0); }

    for (auto &e : s) {
      int a, b;
      tie(a, b) = e;
      cout << i2s[a] << "," << i2s[b] << endl;
    }
    cout << s.size() << endl;
  }

  return 0;
}