原题：https://data.fivk.cn/down.php/9a13cd7c281f6be0d7376606aeea86ee.pdf

试题 E: 出差

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;

const int N = 1e3 + 10, M = 1e4 + 10;
int n, m;
int a, b, c;

int f[N][N];
int dis[M];
int st[M];
int time[N];

int main() {
    memset(f, 0x3f, sizeof f);
    memset(dis, 0x3f, sizeof dis);
    scanf("%d %d", &n, &m);

    for (int i = 1; i <= n; i ++) {
        scanf("%d", &time[i]);
    }

    for (int i = 1; i <= m; i ++) {
        scanf("%d %d %d", &a, &b, &c);
        f[a][b] = min(f[a][b], c + time[b]);
        f[b][a] = min(f[b][a], c + time[a]);
    }

    dis[1] = 0;

    for (int i = 1; i <= n; i ++) {
        int k = -1;
        for (int j = 1; j <= n; j ++) {
            if (!st[j] && (k == -1 || dis[k] > dis[j])) {
                k = j;
            }
        } 
        if (k == -1) break;
        st[k] = true;

        // 更新其余边

        for (int j = 1; j <= n; j ++) {
            if (!st[j]) {
                dis[j] = min(dis[j], dis[k] + f[k][j]);
            }
        } 
    }

    printf("%d  ", dis[n] - time[n]);

    return 0;
}

试题 H: 机房

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;

const int N = 1e5 + 10;

int h[N], e[N], ne[N], idx;
bool st[N];
int cnt[N];
int n, m, a, b;

void add(int a, int b) {
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++;
}

int main() {
    memset(h, -1, sizeof h);
    scanf("%d %d", &n, &m);
    for (int i = 1; i < n; i ++) {
        scanf("%d %d", &a, &b);
        cnt[a] ++;
        cnt[b] ++;
        add(a, b);
        add(b, a);
    }
    int hhh = -1;
    for (int i = 1; i <= n; i ++) {
        if (cnt[i] == 1) {
            hhh = i;
            break;
        }
    }

    int q[N], hh = 0, tt = 1;
    q[0] = hhh;

    while (hh < tt) {
        int t = q[hh ++];
        st[t] = true;
        for (int i = h[t]; i != -1; i = ne[i]) {
            int j = e[i];
            if (!st[j]) q[tt ++] = j;
        }
    }


    for (int i = 1; i <= m; i ++) {
        scanf("%d %d", &a, &b);
        if (a == b) {
            printf("1\n");
            continue;
        }
        bool flag = false;
        int index = 0;
        int ans = 0;
        for (int i = 0; i < tt; i ++) {
            if (q[i] == a || q[i] == b) {
                flag = true;
            }
            if (flag) {
                ans += cnt[q[i]];
                if (index && (q[i] == b || q[i] == a)) {
                    flag = false;
                    break;
                }
                index = 1;
            } 
        }

        printf("%d\n", ans);
    }


    return 0;
}