Problem p01570 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <assert.h>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <stdio.h>
#include <string.h>
#include <string>
#include <vector>

using namespace std;
typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
static const double EPS = 1e-9;
static const double PI = acos(-1.0);

#define REP(i, n) for (int i = 0; i < (int)(n); i++)
#define FOR(i, s, n) for (int i = (s); i < (int)(n); i++)
#define FOREQ(i, s, n) for (int i = (s); i <= (int)(n); i++)
#define FORIT(it, c)                                                           \
  for (__typeof((c).begin()) it = (c).begin(); it != (c).end(); it++)
#define MEMSET(v, h) memset((v), h, sizeof(v))

typedef vector<int> Edges;
typedef vector<Edges> Graph;

int n;
ll len[1200000];
bool root[1200000];
Graph g;
vector<int> order;

int main() {
  while (scanf("%d", &n) > 0) {
    while (n > 300000)
      ;
    MEMSET(root, false);
    g = Graph(n);
    REP(i, n) {
      int p;
      scanf("%lld %d", &len[i], &p);
      if (p != -1) {
        g[p].push_back(i);
      } else {
        root[i] = true;
      }
    }
    REP(i, n) {
      if (!root[i]) {
        continue;
      }
      queue<int> que;
      que.push(i);
      while (!que.empty()) {
        int from = que.front();
        que.pop();
        order.push_back(from);
        FORIT(it, g[from]) {
          int to = *it;
          que.push(to);
        }
      }
    }
    reverse(order.begin(), order.end());
    ll ans = 0;
    REP(i, n) {
      int from = order[i];
      vector<int> lens;
      FORIT(it, g[from]) { lens.push_back(len[*it]); }
      sort(lens.begin(), lens.end());
      ll sum = 0;
      FORIT(it, lens) {
        ans += sum;
        sum += *it;
      }
      len[from] += sum;
    }
    printf("%lld\n", ans);
  }
}

Fixed submission:
#include <algorithm>
#include <assert.h>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <stdio.h>
#include <string.h>
#include <string>
#include <vector>

using namespace std;
typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
static const double EPS = 1e-9;
static const double PI = acos(-1.0);

#define REP(i, n) for (int i = 0; i < (int)(n); i++)
#define FOR(i, s, n) for (int i = (s); i < (int)(n); i++)
#define FOREQ(i, s, n) for (int i = (s); i <= (int)(n); i++)
#define FORIT(it, c)                                                           \
  for (__typeof((c).begin()) it = (c).begin(); it != (c).end(); it++)
#define MEMSET(v, h) memset((v), h, sizeof(v))

typedef vector<int> Edges;
typedef vector<Edges> Graph;

int n;
ll len[1200000];
bool root[1200000];
Graph g;
vector<int> order;

int main() {
  while (scanf("%d", &n) > 0) {
    while (n > 2000000)
      ;
    MEMSET(root, false);
    g = Graph(n);
    REP(i, n) {
      int p;
      scanf("%lld %d", &len[i], &p);
      if (p != -1) {
        g[p].push_back(i);
      } else {
        root[i] = true;
      }
    }
    REP(i, n) {
      if (!root[i]) {
        continue;
      }
      queue<int> que;
      que.push(i);
      while (!que.empty()) {
        int from = que.front();
        que.pop();
        order.push_back(from);
        FORIT(it, g[from]) {
          int to = *it;
          que.push(to);
        }
      }
    }
    reverse(order.begin(), order.end());
    ll ans = 0;
    REP(i, n) {
      int from = order[i];
      vector<int> lens;
      FORIT(it, g[from]) { lens.push_back(len[*it]); }
      sort(lens.begin(), lens.end());
      ll sum = 0;
      FORIT(it, lens) {
        ans += sum;
        sum += *it;
      }
      len[from] += sum;
    }
    printf("%lld\n", ans);
  }
}