【luogu P3275 [SCOI2011]糖果】 题解

题目链接：https://www.luogu.org/problemnew/show/P3275

把不等式 A > B 转化成 A - B >= 1或者 B - A <= -1再差分约束

B - A 不能是 <= 1

2333

// luogu-judger-enable-o2
#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define ll long long
using namespace std;
const int maxn = 100000 + 10;
ll n, m, ans, visnum[maxn], dis[maxn];
bool vis[maxn];
struct edge{
	ll from, to, next, len;
}e[maxn<<2];
ll head[maxn], cnt;
queue<int> q;
/*struct cmp{
	bool operator ()(ll &x, ll &y)
	{
		return dis[x] < dis[y];
	}
};
priority_queue<ll, vector<ll>, cmp> q;*/
inline int read()
{
    int k=0,f=1;
    char c=getchar();
    while(!isdigit(c))
    {
        if(c=='-')f=-1;
        c=getchar();
    }
    while(isdigit(c))
    {
        k=(k<<1)+(k<<3)+c-48;
        c=getchar();
    }
    return k*f;
}
inline void add(ll u, ll v, ll w)
{
	e[++cnt].len = w;
	e[cnt].next = head[u];
	e[cnt].to = v;
	head[u] = cnt;
}
bool SPFA()
{
	while(!q.empty())
	{
		ll now = q.front();q.pop();
		vis[now] = 0;
		if(visnum[now] == n-1) return 1;
		visnum[now]++;
		for(ll i = head[now]; i != -1; i = e[i].next)
		{
			if(dis[e[i].to] > dis[now] + e[i].len)
			{
				dis[e[i].to] = dis[now] + e[i].len;
				if(!vis[e[i].to])
				{
					vis[e[i].to] = 1;
					q.push(e[i].to);
				}
			}
		}
	}
	return 0;
}
int main()
{
	memset(head, -1, sizeof(head));
	//scanf("%lld%lld",&n,&m);
	n = read(); m = read();
	for(ll i = 1; i <= m; i++)
	{
		ll opt, u, v;
		//scanf("%lld%lld%lld",&opt,&u,&v);
		opt = read(); u = read(); v = read();
		if(opt == 1)
		{
			add(u, v, 0);
			add(v, u, 0);
		}
		if(opt == 2)
		{
			if(u == v)
			{
				printf("-1\n");
				return 0;
			}
			add(u, v, -1);
		}
		if(opt == 3)
		{
			add(v, u, 0);
		}
		if(opt == 4)
		{
			if(u == v)
			{
				printf("-1\n");
				return 0;
			}
			add(v, u, -1);
		}
		if(opt == 5)
		{
			add(u, v, 0);
		}
	}
	for(ll i = n; i >= 1; i--)
	{
		add(0, i, -1);
		dis[i] = 0x7fffffff;
	}
	int s = 0;
	q.push(s);
	dis[s] = 0; vis[s] = 1;
	if(SPFA())
	{
		printf("-1\n");
		return 0;
	}
	else
	{
		for(int i = 1; i <= n; i++)
		ans += dis[i];
		printf("%lld\n",-ans);
		return 0;
	}
}