hihoCoder#1050 树中的最长路

原题地址

根据提示做即可，总感觉数据结构用的不好，以后看看大神都是怎么用数组存树的。

#include <iostream>
#include <vector>

using namespace std;

struct Node {
  int first;
  int second;
  bool rootp;
  vector<int> children;
  Node() : first(0), second(0), rootp(true) {}
};

int bestpath = 0;

void traverse(Node *nodes, int root) {
  if (nodes[root].children.empty()) {
    nodes[root].first = 0;
    nodes[root].second = 0;
    return;
  }

  int first = 0;
  int second = 0;

  for (auto c : nodes[root].children) {
    traverse(nodes, c);
    second = max(second, min(first, nodes[c].first));
    first = max(first, nodes[c].first);
  }
  if (nodes[root].children.size() == 1)
    second = -1;

  nodes[root].first = first + 1;
  nodes[root].second = second + 1;
  bestpath = max(bestpath, nodes[root].first + nodes[root].second);
}

int main() {
  int N;
  int a, b;
  Node nodes[100010];

  cin >> N;
  for (int i = 1; i < N; i++) {
    cin >> a >> b;
    nodes[a - 1].children.push_back(b - 1);
    nodes[b - 1].rootp = false;
  }

  for (int i = 0; i < N; i++) {
    if (nodes[i].rootp) {
      traverse(nodes, i);
      break;
    }
  }

  cout << bestpath << endl;

  return 0;
}