Friend Chains

题目链接

求任意点对的最短距离的最大值

#include <iostream>
#include <queue>
#include <map>
#include <vector>
#include <cstring>
#include <algorithm>
using namespace std;
int N, M;
map<string, int> rap;
vector<vector<int>> v;
int INF = 0x3f3f3f3f;

int bfs()
{
    
    

    int ans = -1;
    for (int i = 0; i < N; i++)
    {
    
    
        // i点 到所有点的最短距离
        // 需要找到这些点中的最远的一个点

        queue<int> q;
        int dp[1005] = {
    
    0};
        dp[i] = 1;
        q.push(i);
        int dist[1005];
        fill(dist, dist + 1004, -INF);
        dist[i] = 0;

        while (!q.empty())
        {
    
    
            auto x = q.front();
            q.pop();
            for (auto e : v[x])
            {
    
    
                if (dp[e] == 0)
                {
    
    
                    dp[e] = 1;
                    q.push(e);
                    dist[e] = dist[x] + 1;
                }
            }
        }
        int anst = -INF;
        for (int i = 0; i < N; i++)
        {
    
    
            if (dist[i] == -INF)
            {
    
    
                anst = -1;
                break;
            }
            anst = max(dist[i], anst);
        }

        // 在这些点的最短路径中 找到最长的路 才能确定任意两人的朋友链长度
        ans = max(anst, ans);
    }
    return ans;
}
int main()
{
    
    
    while (cin >> N && N != 0)
    {
    
    
        string s;
        v.clear();
        v.resize(N + 10);
        for (int i = 0; i < N; i++)
        {
    
    
            char c[15];
            scanf("%s", c);
            rap[(string)c] = i;
        }
        cin >> M;
        while (M--)
        {
    
    
            char x[15], y[15];
            scanf("%s%s", x, y);
            int nx = rap[x];
            int ny = rap[y];
            v[nx].push_back(ny);
            v[ny].push_back(nx);
        }

        // cout << bfs() << endl;
        printf("%d\n", bfs());
    }
    return 0;
}