一本通1512：排队布局

使用SPFA算法求解带权无向图的最短路径问题

最新推荐文章于 2025-12-07 17:14:34 发布

原创最新推荐文章于 2025-12-07 17:14:34 发布 · 432 阅读

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#图论 #c++ #算法

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <queue>
#include <cstdlib>
using namespace std;
const int INF = 1000000005;
const int MAXN = 1005;
struct edge {
    int to, wei;
};
int n, ml, md;
vector<edge> adj[MAXN];
int dis[MAXN], vis[MAXN], cnt[MAXN];
bool flag = true;
void SPFA(int st) {
    for (int i = 1; i <= n; i ++)
        dis[i] = INF;

    memset(vis, false, sizeof(vis));
    memset(cnt, 0, sizeof(cnt));
    queue<int> q;
    q.push(st);
    vis[st] = true;
    dis[st] = 0;
    cnt[st] = 1;

    while (!q.empty()) {
        int u = q.front();
        q.pop();
        vis[u] = false;

        for (int i = 0; i < adj[u].size(); i ++) {
            int v = adj[u][i].to;
            int w = adj[u][i].wei;

            if (dis[v] > dis[u] + w) {
                dis[v] = dis[u] + w;

                if (!vis[v]) {
                    if (cnt[v] > n) {
                        flag = false;
                        return;
                    }

                    vis[v] = true;
                    q.push(v);
                    cnt[v] ++;
                }
            }
        }
    }

    return;
}
int main() {
    scanf("%d%d%d", &n, &ml, &md);

    while (ml --) {
        int a, b, di;
        scanf("%d%d%d", &a, &b, &di);
        adj[a].push_back(edge{b, di});
    }

    while (md --) {
        int a, b, di;
        scanf("%d%d%d", &a, &b, &di);
        adj[b].push_back(edge{a, -di});
    }

    for (int i = 1; i < n; i ++)
        adj[i + 1].push_back(edge{i, 0});

    for (int i = 1; i <= n; i ++)
        adj[0].push_back(edge{i, 0});
    SPFA(0);

    if (!flag) {
        puts("-1");
        return 0;
    }

    SPFA(1);

    if (dis[n] >= INF) {
        puts("-2");
        return 0;
    }

    printf("%d\n", dis[n]);
    return 0;
}