hdu 4607 Park Visit(bfs)

题目链接:hdu 4607 Park Visit

解题思路

超过树直径的部分要走两遍。

代码

#include <cstdio>
#include <cstring>
#include <vector>
#include <queue>
#include <algorithm>

using namespace std;
const int maxn = 1e5 + 5;

int N, Q, D[maxn];
vector<int> G[maxn];

void init () {
    scanf("%d%d", &N, &Q);
    for (int i = 1; i <= N; i++)
        G[i].clear();

    int u, v;
    for (int i = 1; i < N; i++) {
        scanf("%d%d", &u, &v);
        G[u].push_back(v);
        G[v].push_back(u);
    }
}

int solve () {
    queue<int> que;

    que.push(1);
    int u = 1;
    memset(D, -1, sizeof(D));
    D[u] = 0;

    while (!que.empty()) {
        u = que.front();
        que.pop();

        for (int i = 0; i < G[u].size(); i++) {
            int v = G[u][i];
            if (D[v] != -1) continue;
            D[v] = D[u] + 1;
            que.push(v);
        }
    }

    que.push(u);
    memset(D, -1, sizeof(D));
    D[u] = 0;
    while (!que.empty()) {
        u = que.front();
        que.pop();

        for (int i = 0; i < G[u].size(); i++) {
            int v = G[u][i];
            if (D[v] != -1) continue;
            D[v] = D[u] + 1;
            que.push(v);
        }
    }
    return D[u] + 1;
}

int main () {
    int cas;
    scanf("%d", &cas);
    while (cas--) {
        init();
        int n = solve(), x;
        while (Q--) {
            scanf("%d", &x);
            if (x <= n) printf("%d\n", x-1);
            else printf("%d\n", n-1 + (x-n) * 2);
        }
    }
    return 0;
}

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