UVA - 11280 Flying to Fredericton(SPFA)

题目大意：给出N个点，M条线，Q个询问，问从起点到终点，最多经过k个点的最短线路

解题思路：spfa直接跑，然后纪录最短路的数组加一个维度，纪录经过几个点就可以了，还是挺水的

#include <cstdio>
#include <cstring>
#include <map>
#include <iostream>
#include <queue>
using namespace std;

#define N 110
#define M 1010
#define INF 0x3f3f3f3f

struct Edge{
    int u, v, next, c;
}E[M];

struct Node {
    int u, time;
    Node() {}
    Node(int u, int time): u(u), time(time) {}
}n1, n2;

map<string, int> city;
int n, m, tot, q;
int head[N], d[N][N];
bool vis[N][N];

void AddEdge(int u, int v, int c) {
    E[tot].v = v;
    E[tot].c = c;
    E[tot].next = head[u];
    head[u] = tot++;
}

void init() {
    city.clear();
    scanf("%d", &n);
    string a, b;
    for (int i = 1; i <= n; i++) {
        cin >> a;
        city[a] = i;
    }

    memset(head, -1, sizeof(head));
    tot = 0;

    scanf("%d", &m);
    int c;
    for (int i = 0; i < m; i++) {
        cin >> a >> b >> c;
        AddEdge(city[a], city[b], c);
    }
}

int s, t;
void spfa() {
    memset(d, 0x3f, sizeof(d));
    memset(vis, 0, sizeof(vis));
    queue<Node> Q;
    Q.push(Node(s,0));
    d[s][0] = 0;

    while (!Q.empty()) {
        n1 = Q.front();
        Q.pop();

        int u = n1.u, time = n1.time;
        for (int i = head[n1.u]; ~i; i = E[i].next) {
            int v = E[i].v;
            if (d[u][time] + E[i].c < d[v][time + 1]) {
                d[v][time + 1] = d[u][time] + E[i].c;
                if (!vis[v][time + 1]) {
                    vis[v][time + 1] = true;
                    Q.push(Node(v, time + 1));
                }
            }
        }
    }
}

void solve() {
    s = city["Calgary"]; t = city["Fredericton"];
    spfa();

    scanf("%d", &q);
    int Max;
    while (q--) {
        scanf("%d", &Max);
        Max = min(Max, n);
        int ans = INF;
        for (int i = 0; i <= Max + 1; i++)
            ans = min(ans, d[t][i]);
        if (ans == INF)
            printf("No satisfactory flights\n");
        else
            printf("Total cost of flight(s) is $%d\n", ans);
    }

}

int main() {
    int test, cas = 1;
    bool flag = false;
    scanf("%d", &test);
    while (test--) {
        if (flag)
            printf("\n");
        flag = true;
        printf("Scenario #%d\n", cas++);
        init();
        solve();
    }
    return 0;
}

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