Problem p00909 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>

using namespace std;

inline int toInt(string s) {
  int v;
  istringstream sin(s);
  sin >> v;
  return v;
}
template <class T> inline string toString(T x) {
  ostringstream sout;
  sout << x;
  return sout.str();
}
template <class T> inline T sqr(T x) { return x * x; }

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;

#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define pb push_back
#define mp make_pair
#define each(i, c)                                                             \\
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define exist(s, e) ((s).find(e) != (s).end())
#define range(i, a, b) for (int i = (a); i < (b); ++i)
#define rep(i, n) range(i, 0, n)
#define clr(a, b) memset((a), (b), sizeof(a))
#define dump(x) cerr << #x << " = " << (x) << endl;
#define debug(x)                                                               \\
  cerr << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \\
       << " " << __FILE__ << endl;

const double eps = 1e-10;
const double pi = acos(-1.0);
const ll INF = 1LL << 62;
const int inf = 1 << 29;

const int nmax = 100010;
int par[nmax], ranks[nmax], weight[nmax];

void init(int n) { rep(i, n) par[i] = i, ranks[i] = 0, weight[i] = 0; }
int find(int x, int &w) {
  if (par[x] == x)
    return x;
  else {
    w += weight[x];
    return find(par[x], w);
  }
}

void unite(int a, int b, int c) {
  int wa = 0, wb = 0;
  int pa = find(a, wa);
  int pb = find(b, wb);
  if (ranks[pa] < ranks[pb]) {
    par[pa] = pb;
    weight[pa] = wb - wa + c;
  } else {
    par[pb] = pa;
    weight[pb] = wa - wb - c;
    if (ranks[pa] == ranks[pb])
      ranks[pa]++;
  }
}

bool same(int a, int b, int &ans) {
  int wa = 0, wb = 0;
  int pa = find(a, wa);
  int pb = find(b, wb);
  ans = wa - wb;
  return pa == pb;
}

int main(void) {
  int n, m;
  while (cin >> n >> m, n) {
    init(n);
    rep(i, m) {
      char cmd;
      cin >> cmd;
      if (cmd == '!') {
        int a, b, c;
        cin >> a >> b >> c;
        unite(a - 1, b - 1, c);
      } else {
        int a, b, ans;
        cin >> a >> b;
        if (same(a - 1, b - 1, ans))
          cout << ans << endl;
        else
          cout << "UNKNOWN" << endl;
      }
    }
  }
  return 0;
}

Error: TLE

Fixed submission:

#include <bits/stdc++.h>

using namespace std;

inline int toInt(string s) {
  int v;
  istringstream sin(s);
  sin >> v;
  return v;
}
template <class T> inline string toString(T x) {
  ostringstream sout;
  sout << x;
  return sout.str();
}
template <class T> inline T sqr(T x) { return x * x; }

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;

#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define pb push_back
#define mp make_pair
#define each(i, c)                                                             \\
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define exist(s, e) ((s).find(e) != (s).end())
#define range(i, a, b) for (int i = (a); i < (b); ++i)
#define rep(i, n) range(i, 0, n)
#define clr(a, b) memset((a), (b), sizeof(a))
#define dump(x) cerr << #x << " = " << (x) << endl;
#define debug(x)                                                               \\
  cerr << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \\
       << " " << __FILE__ << endl;

const double eps = 1e-10;
const double pi = acos(-1.0);
const ll INF = 1LL << 62;
const int inf = 1 << 29;

const int nmax = 100010;
int par[nmax], ranks[nmax], weight[nmax];

void init(int n) { rep(i, n) par[i] = i, ranks[i] = 0, weight[i] = 0; }
int find(int x, int &w) {
  if (par[x] == x)
    return x;
  else {
    w += weight[x];
    return find(par[x], w);
  }
}

void unite(int a, int b, int c) {
  int wa = 0, wb = 0;
  int pa = find(a, wa);
  int pb = find(b, wb);
  if (ranks[pa] < ranks[pb]) {
    par[pa] = pb;
    weight[pa] = wb - wa + c;
  } else {
    par[pb] = pa;
    weight[pb] = wa - wb - c;
    if (ranks[pa] == ranks[pb])
      ranks[pb]++;
  }
}

bool same(int a, int b, int &ans) {
  int wa = 0, wb = 0;
  int pa = find(a, wa);
  int pb = find(b, wb);
  ans = wa - wb;
  cout << " " << pa << " " << pb << endl;
  return pa == pb;
}

int main(void) {
  int n, m;
  while (cin >> n >> m, n) {
    init(n);
    rep(i, m) {
      char cmd;
      cin >> cmd;
      if (cmd == '!') {
        int a, b, c;
        cin >> a >> b >> c;
        unite(a - 1, b - 1, c);
      } else {
        int a, b, ans;
        cin >> a >> b;
        if (same(a - 1, b - 1, ans))
          cout << ans << endl;
        else
          cout << "UNKNOWN" << endl;
      }
    }
  }
  return 0;
}