Luogu1993 小K的农场（差分约束）

\(if \ a - b <= c, AddEdge(b, a, c)\)

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;

}

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Luogu1993 小K的农场（差分约束）

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Luogu1993 小K的农场 （差分约束）

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Luogu1993 小K的农场（差分约束）