Problem p03166 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <bits/stdc++.h>
#include <cmath>
#include <cstdio>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <utility>
#include <vector>

#define fir first
#define sec second
#define sz(s) (s).size();
#define pb push_back
#define get(n) scanf("%d", &n);
#define gets(s)                                                                \
  string s;                                                                    \
  cin >> (s);
#define prfi(n) printf("%d", &n);
#define prfd(n) printf("%lf", &n);
#define All(s) (s).begin(), (s).end()
#define rep(i, j, k) for (int(i) = (j); (i) <= (k); (i)++)
#define repdown(i, j, k) for (int(i) = (j); (i) >= (k); (i)--)
#define dump(x) std::cout << #x << " = " << (x) << std::endl;
#define debug(x)                                                               \
  cout << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \
       << " " << __FILE__ << endl;

using ll = long long;
using vi = std::vector<int>;
using vvi = std::vector<vi>;
using vll = std::vector<ll>;
using vvll = std::vector<vll>;
using vd = std::vector<double>;
using vvd = std::vector<vd>;
using qi = std::queue<int>;
using vpii = std::vector<std::pair<int, int>>;
using namespace std;

const int Mod = (1e9) + 7;
const int max_n = 3 * (1e5) + 1;
const int max_m = 83 * (1e5) + 1;
const int INF = 10241024;
long double INFD = 100100100;

//_____________________________________Templates_________________________________________//

template <class T1, class T2> inline void chmin(T1 &a, T2 b) {
  if (a > b)
    a = b;
}
template <class T1, class T2> inline void chmax(T1 &a, T2 b) {
  if (a < b)
    a = b;
}

// mainly use for dynamic prog
template <class T1, class T2> void update(T1 &a, T2 b) {
  a += b;
  if (a > Mod)
    a %= Mod;
}

inline void IN(void) { return; }

template <typename First, typename... Rest>
void IN(First &first, Rest &...rest) {
  cin >> first;
  IN(rest...);
  return;
}

inline void OUT(void) {
  cout << "\n";
  return;
}

template <typename First, typename... Rest>
void OUT(First first, Rest... rest) {
  cout << first << " ";
  OUT(rest...);
  return;
}

//_____________________array calc____________________________________//
/*
vvi mul(vvi &A, vvi &B){
  vvi C(A.size(), vi(B.size()))
  rep(i,A.size()){
    rep(j,B.size()){
      rep(k,B[0].size()){
        C[i][j] = (C[i][j] A[i][k] + B[k][j]) % Mod;
      }
    }
  }

  return C;
}

vvi pow(vvi A, ll n){
  vvi B(A.size(), vi(A.size()));
  rep(i=0;i<A.size();i++){
    B[i][i] = 1;
  }

  while (n >0){
    if (n & 1) B = mul(B, A);
    A = mul(A, A);
    n = n >> 1;
  }
  return B;
}
*/
//_____________________Bynary Indexed Tree __________________________//
/*
const max_st = (1 << 15) - 1;
int bit[max_st];
int sum (int i){
  int s = 0;
  while(i > 0){
    s += bit[i];
    i -= i & -i;
  }
  return s;
}

void add(int i, int x){
  while(i <= n){
    bit[i] += x;
    i += i & -i;
  }
}
*/
//_____________________　following sorce code_________________________//

vvi dist;
vi li;
vi lis;
void dfs(int u) {
  if (li[u] != 0)
    return;
  lis[u] = 1;
  for (auto c : dist[u])
    dfs(c);
  li.pb(u);
}

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

  int n, m;
  IN(n, m);
  dist.resize(n);
  li.resize(n);
  lis.resize(n);
  rep(i, 0, m - 1) {
    int a, b;
    IN(a, b);
    a--;
    b--;
    dist[a].push_back(b);
  }
  vi dp(n);
  int ans = 0;
  rep(i, 0, n - 1) dfs(i);
  for (auto c : li) {
    for (auto d : dist[c]) {
      chmax(dp[c], dp[d] + 1);
    }
    chmax(ans, dp[c]);
  }
  OUT(ans);
  return 0;
}

Fixed submission:
#include <algorithm>
#include <bits/stdc++.h>
#include <cmath>
#include <cstdio>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <utility>
#include <vector>

#define fir first
#define sec second
#define sz(s) (s).size();
#define pb push_back
#define get(n) scanf("%d", &n);
#define gets(s)                                                                \
  string s;                                                                    \
  cin >> (s);
#define prfi(n) printf("%d", &n);
#define prfd(n) printf("%lf", &n);
#define All(s) (s).begin(), (s).end()
#define rep(i, j, k) for (int(i) = (j); (i) <= (k); (i)++)
#define repdown(i, j, k) for (int(i) = (j); (i) >= (k); (i)--)
#define dump(x) std::cout << #x << " = " << (x) << std::endl;
#define debug(x)                                                               \
  cout << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \
       << " " << __FILE__ << endl;

using ll = long long;
using vi = std::vector<int>;
using vvi = std::vector<vi>;
using vll = std::vector<ll>;
using vvll = std::vector<vll>;
using vd = std::vector<double>;
using vvd = std::vector<vd>;
using qi = std::queue<int>;
using vpii = std::vector<std::pair<int, int>>;
using namespace std;

const int Mod = (1e9) + 7;
const int max_n = 3 * (1e5) + 1;
const int max_m = 83 * (1e5) + 1;
const int INF = 10241024;
long double INFD = 100100100;

//_____________________________________Templates_________________________________________//

template <class T1, class T2> inline void chmin(T1 &a, T2 b) {
  if (a > b)
    a = b;
}
template <class T1, class T2> inline void chmax(T1 &a, T2 b) {
  if (a < b)
    a = b;
}

// mainly use for dynamic prog
template <class T1, class T2> void update(T1 &a, T2 b) {
  a += b;
  if (a > Mod)
    a %= Mod;
}

inline void IN(void) { return; }

template <typename First, typename... Rest>
void IN(First &first, Rest &...rest) {
  cin >> first;
  IN(rest...);
  return;
}

inline void OUT(void) {
  cout << "\n";
  return;
}

template <typename First, typename... Rest>
void OUT(First first, Rest... rest) {
  cout << first << " ";
  OUT(rest...);
  return;
}

//_____________________array calc____________________________________//
/*
vvi mul(vvi &A, vvi &B){
  vvi C(A.size(), vi(B.size()))
  rep(i,A.size()){
    rep(j,B.size()){
      rep(k,B[0].size()){
        C[i][j] = (C[i][j] A[i][k] + B[k][j]) % Mod;
      }
    }
  }

  return C;
}

vvi pow(vvi A, ll n){
  vvi B(A.size(), vi(A.size()));
  rep(i=0;i<A.size();i++){
    B[i][i] = 1;
  }

  while (n >0){
    if (n & 1) B = mul(B, A);
    A = mul(A, A);
    n = n >> 1;
  }
  return B;
}
*/
//_____________________Bynary Indexed Tree __________________________//
/*
const max_st = (1 << 15) - 1;
int bit[max_st];
int sum (int i){
  int s = 0;
  while(i > 0){
    s += bit[i];
    i -= i & -i;
  }
  return s;
}

void add(int i, int x){
  while(i <= n){
    bit[i] += x;
    i += i & -i;
  }
}
*/
//_____________________　following sorce code_________________________//

vvi dist;
vi li;
vi lis;
void dfs(int u) {
  if (lis[u] != 0)
    return;
  lis[u] = 1;
  for (auto c : dist[u])
    dfs(c);
  li.pb(u);
}

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

  int n, m;
  IN(n, m);
  dist.resize(n);
  li.resize(n);
  lis.resize(n);
  rep(i, 0, m - 1) {
    int a, b;
    IN(a, b);
    a--;
    b--;
    dist[a].push_back(b);
  }
  vi dp(n);
  int ans = 0;
  rep(i, 0, n - 1) dfs(i);
  for (auto c : li) {
    for (auto d : dist[c]) {
      chmax(dp[c], dp[d] + 1);
    }
    chmax(ans, dp[c]);
  }
  OUT(ans);
  return 0;
}