Luogu1993 小K的农场 （差分约束）

Posted 2022-08-22 bingoyes

\(if \ a - b <= c, AddEdge(b, a, c)\)
Be careful, MLE is not good.

#include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>
#define R(a,b,c) for(register int a = (b); (a) <= (c); ++(a))
#define nR(a,b,c) for(register int a = (b); (a) >= (c); --(a))
#define Fill(a,b) memset(a, b, sizeof(a))
#define Max(a,b) ((a) > (b) ? (a) : (b))
#define Min(a,b) ((a) < (b) ? (a) : (b))
#define Swap(a,b) ((a) ^= (b) ^= (a) ^= (b))

#define ON_DEBUGG

#ifdef ON_DEBUGG

#define D_e_Line printf("\n----------\n") 
#define D_e(x) cout << (#x) << " : " << x << endl
#define Pause() system("pause")
#define FileOpen() freopen("in.txt", "r", stdin)

#else

#define D_e_Line ;
#define D_e(x) ;
#define Pause() ;
#define FileOpen() ;

#endif
using namespace std;
struct ios
    template<typename ATP>inline ios& operator >> (ATP &x)
        x = 0; int f = 1; char ch;
        for(ch = getchar(); ch < '0' || ch > '9'; ch = getchar()) if(ch == '-') f = -1;
        while(ch >= '0' && ch <= '9') x = x * 10 + (ch ^ '0'), ch = getchar();
        x *= f;
        return *this;
    
io;

const int N = 20007;

struct Edge
    int nxt, pre, w;
e[N << 1];
int head[N], cntEdge;
inline void add(int u, int v, int w)
    e[++cntEdge] = (Edge) head[u], v, w, head[u] = cntEdge;


int vis[N], dis[N];
inline bool SPFA(int u)
    vis[u] = true;
    for(register int i = head[u]; i; i = e[i].nxt)
        if(dis[e[i].pre] > dis[u] + e[i].w)
            dis[e[i].pre] = dis[u] + e[i].w;
            if(vis[e[i].pre] || SPFA(e[i].pre))
                return true;
            
        
    
    vis[u] = false;
    return false;


int main()
//FileOpen();
    int n, m;
    io >> n >> m;
    
    R(i,1,m)
        int opt;
        io >> opt;
        if(opt == 1)
            int x, y, w;
            io >> x >> y >> w;
            add(x, y, -w);
        
        else if(opt == 2)
            int x, y, w;
            io >> x >> y >> w;
            add(y, x, w);   
        
        else if(opt == 3)
            int x, y;
            io >> x >> y;
            add(x, y, 0);
            add(y, x, 0);
        
    
    
    R(i,1,n)
        add(0, i, 0); // this sentence caused MLE !
        dis[i] = 0x3f3f3f3f;
    
    
    if(SPFA(0) == false)
        printf("Yes\n");
    
    else
        printf("No\n");
    
    return 0;