HDU 4460 Friend Chains

合集 - HDU(13)

1.HDU 1312 Red And Black2024-07-092.HDU 1240 Asteroids!2024-07-10

3.HDU 4460 Friend Chains2024-07-11

4.HDU 2037 今年暑假不AC2024-07-125.HDU 2570 迷瘴2024-07-146.HDU 1213 How Many Tables2024-07-127.HDU 1789 Doing Homework again2024-07-168.HDU 1020 Encoding2024-07-269.HDU 4334 Trouble2024-08-0110.HDU 2999 Stone Game, Why are you always there?2024-08-1611.HDU 3980 Paint Chain2024-08-1612.HDU 2873 Bomb Game2024-08-1613.HDU 3590 PP and QQ2024-08-16

收起

题目链接：HDU 4460【Friend Chains】

---

---

思路

       哈希使得每个人都有一个对应的数字，然后用邻接表存储，然后使用BFS搜索出最长的友人链。注意每一次搜索都需要初始化vis标记数组，在每一组测试样例完成后需要将mp哈希map和邻接表ve初始化为空，否则会影响计算。注意当出现两个联通块时需要输出-1。

---

代码

#include <iostream>
#include <algorithm>
#include <cstring>
#include <queue>
#include <map>
using namespace std;
const int N = 1e3 + 10;
 
int n, m, k, res, flag;
map<string, int> mp;
vector<int>ve[N];
bool vis[N];
 
struct node {
  int x, step;
};
 
void bfs(int x) {
  vis[x] = true;
  queue<node> q;
  q.push({x, 0});
 
  while (!q.empty()) {
    node start = q.front();
    q.pop();
    for (auto it : ve[start.x]) {
      if (vis[it] == true)
        continue;
      vis[it] = true;
      q.push({it, start.step + 1});
    }
    res = max(res, start.step);
  }
  for (int i = 1; i <= n; i++) {
    if (vis[i] == 0) {
      flag = 1;
      return;
    }
  }
}
 
int main() {
  while (cin >> n){
    mp.clear();
 
    if (n == 0)
      break;
 
    for (int i = 1; i <= n; i++) {
      ve[i].clear();
      string s;
      cin >> s;
      mp[s] = i;
    }
 
    cin >> m;
    for (int i = 1; i <= m; i++) {
      string start, target;
      cin >> start >> target;
      ve[mp[start]].push_back(mp[target]);
      ve[mp[target]].push_back(mp[start]);
    }
    int start = 0;
    for (int i = 1; i <= n; i++) {
      memset(vis, 0, sizeof vis);
      bfs(i);
      if (flag) break;
    }
    if (flag)
      cout << -1 << endl;
    else
      cout << res << endl;
  }
  return 0;
}