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:

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#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;
}

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I want to konw how:

Code:

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

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is transfered to

Code:

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

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it is really confusing......

Code:

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

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also g was declared as

Code:

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

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Please help

Quote:

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Originally Posted by enakta13

I want to konw how:

Code:

---

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

---

is transfered to

Code:

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

---

it is really confusing......

Code:

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

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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.

Quote:

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also g was declared as

Code:

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

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Please help

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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.

Quote:

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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

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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.

Quote:

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Originally Posted by enakta13

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

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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.

Quote:

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Originally Posted by enakta13

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

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