In vector what does it mean?

G[u].push back(v);

here G[5] is a vector
u,v are int

vector - C++ Reference

Code:

#include <algorithm>
#include <iostream>

#include <vector>


using namespace std;


const int MAXN = 100;

int A[MAXN], B[MAXN];

vector<int> g[MAXN];

bool second_high_to_low(pair<int, int> a, pair<int, int> b){
  if (a.second != b.second) return a.second > b.second;
  return a.first < b.first;
}

pair<int, int> f(int u, int dad = -1){
  vector< pair<int, int> > p;
  for (int i = 0; i < g[u].size(); ++i){
    int v = g[u][i];
    if (v == dad) continue;

    p.push_back( f(v, u) );
  }

  sort(p.begin(), p.end(), second_high_to_low);

  int total = A[u];
  int inhand = A[u] - B[u];
  for (int i = 0; i < p.size(); ++i){
    if (inhand > p[i].first){
      inhand -= p[i].first - p[i].second;
    }else{
      total += p[i].first - inhand;
      inhand = p[i].second;
    }
  }
  return make_pair(total, inhand);
}

int main(){
  int n, Case = 1;
  while (cin >> n){
    if (n == 0) break;
    cout << "Case " << Case++ << ": ";

    for (int i = 0; i < n; ++i){
      int x, y, z;
      cin >> x >> y >> z;
      A[i] = x;
      B[i] = y + z;
      A[i] = max(A[i], B[i]);

      g[i].clear();
    }

    for (int i = 0; i < n - 1; ++i){
      int u, v;
      cin >> u >> v;
      u--, v--;
      g[u].push_back(v);
      g[v].push_back(u);
    }


    int ans = 3000;
    for (int i = 0; i < n; ++i){

      pair<int, int> p = f(i);

      ans = min(ans, p.first);

    }

    cout << ans << endl;
  }
  return 0;
}

I want to konw how:

Code:

pair<int, int> p = f(i);

is transfered to

Code:

pair<int, int> f(int u, int dad = -1){

it is really confusing......

Code:

how f(i) becomes f(int u,int dad=-1)?

also g was declared as

Code:

vector<int> g[MAX];
how come it becomes g[u][i];?

Please help

Originally Posted by enakta13

I want to konw how:

Code:

pair<int, int> p = f(i);

is transfered to

Code:

pair<int, int> f(int u, int dad = -1){

it is really confusing......

Code:

how f(i) becomes f(int u,int dad=-1)?

It's a C++ feature called default arguments. Unless you provide a different argument for dad, it will be -1 in the function. What's the reason, you think? A default argument is a good way to add functionality or a fix to a function working in existing code without breaking existing code.

also g was declared as

Code:

vector<int> g[MAX];
how come it becomes g[u][i];?

Please help

It's inherent in the type of g. An array of vectors can be indexed that way.

Please help yourself to the detailed reference on the web you were linked earlier.

Originally Posted by whiteflags

It's a C++ feature called default arguments. Unless you provide a different argument for dad, it will be -1 in the function. What's the reason, you think? A default argument is a good

Maybe you didn't understand the question!He clearly says how f(i) becomes...

He does not question about default values.He asks about vectors in his post

You're an idiot. He asks about both vectors and default arguments in his post. All you have to do is read his code to notice this, but I will explain my answer.

f() is a function.
pair<int, int> is the return value, f is the function name, and there's the parameter list "(int u, int dad = -1)". dad = -1 in this context is a default argument. You can also see the function body.

Originally Posted by enakta13

how f(i) becomes f(int u,int dad=-1)?

I mean, if I read the question wrong, you're welcome to put some effort in and actually correct me.

But I also answer his other question.

Originally Posted by enakta13

how come it becomes g[u][i];?

Perhaps I didn't answer it well, but what could I do? It would be nice if he knew more words.