洛谷P1993 小K的农场

那群人除了会卡spfa还会干什么！

我优雅的bfs spfa 居然T了一个点！不能忍！

 

// luogu-judger-enable-o2
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
using namespace std;
const int MAXN = 1e4 + 20;

int N, M;
struct Edge
{
    int to, cost;
};vector<Edge> g[MAXN];

int cnt[MAXN], dis[MAXN];
bool inq[MAXN];

bool spfa(){
    queue<int> q;
    memset(dis, -0x3f, sizeof(dis));
    memset(cnt, false, sizeof(cnt));
    dis[0] = 0; q.push(0);
    while(!q.empty())
    {
        int u = q.front(); q.pop(); inq[u] = false;
        for(int i = 0; i < (int) g[u].size(); i++){
            Edge &e = g[u][i];
            if(dis[e.to] < dis[u] + e.cost){
                dis[e.to] = dis[u] + e.cost;
                cnt[e.to] = cnt[u] + 1;
                if(cnt[e.to] > N) return false;
                if(!inq[e.to]) inq[e.to] = true, q.push(e.to);
            }
        }
    }
    return true;
}

int main()
{
    cin>>N>>M;
    for(int i = 1, u, v, c, t; i <= M; i++){
        scanf("%d%d%d",&t, &u, &v);
        if(t == 1) scanf("%d", &c), g[v].push_back((Edge){u, c});
        else if(t == 2) scanf("%d", &c), g[v].push_back((Edge){u, -c});
        else g[u].push_back((Edge){v, 0}), g[v].push_back((Edge){u, 0});
    }
    for(int i = 1; i <= N; i++) g[0].push_back((Edge){i, 0});
    if(!spfa()) puts("No");
    else puts("Yes");
    return 0;
}

 以下为AC的dfs版spfa

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
using namespace std;
const int MAXN = 1e4 + 20;

int N, M;
struct Edge
{
    int to, cost;
};vector<Edge> g[MAXN];

bool vis[MAXN];
int dis[MAXN];

bool spfa(int cur){
    vis[cur] = true;
    for(int i = 0; i < (int) g[cur].size(); i++){
        Edge &e = g[cur][i];
        if(dis[e.to] < dis[cur] + e.cost){
            if(vis[e.to]) return true;
            dis[e.to] = dis[cur] + e.cost;
            if(spfa(e.to)) return true;
        }
    }
    vis[cur] = false ;
    return false;
}

int main()
{
    //freopen("p1993.in", "r", stdin);
    cin>>N>>M;
    for(int i = 1, u, v, c, t; i <= M; i++){
        scanf("%d%d%d",&t, &u, &v);
        if(t == 1) scanf("%d", &c), g[v].push_back((Edge){u, c});
        else if(t == 2) scanf("%d", &c), g[v].push_back((Edge){u, -c});
        else g[u].push_back((Edge){v, 0}), g[v].push_back((Edge){u, 0});
    }
    for(int i = 1; i <= N; i++) g[0].push_back((Edge){i, 0});
    memset(dis, -0x3f, sizeof(dis)); dis[0] = 0;
    if(spfa(0)) puts("No");
    else puts("Yes");
    return 0;
}