uvalive 4885 差分约束

来源：互联网发布：宜昌学历网络教育报名编辑：程序博客网时间：2024/06/14 23:25

就是差分约束的裸题，因为今天比赛时间来不及，没搞完。

贴个模板。具体关于差分约束系统的解释请搜其他博客。

我用最长路和最短路都实现了一遍。

对于(>=)的系统，求最长路，求最小值。

对于(<=)的系统，求最短路，求最大值。

然后SPFA之前，我们可以将所有的点都入队。这样就相当于一个超级源点了。

最长路：

#include <set>#include <map>#include <stack>#include <cmath>#include <queue>#include <cstdio>#include <string>#include <vector>#include <iomanip>#include <cstring>#include <iostream>#include <algorithm>#define Max 2505#define FI first#define SE second#define ll long long#define PI acos(-1.0)#define inf 0x3fffffff#define LL(x) ( x << 1 )#define bug puts("here")#define PII pair<int,int>#define RR(x) ( x << 1 | 1 )#define mp(a,b) make_pair(a,b)#define mem(a,b) memset(a,b,sizeof(a))#define REP(i,s,t) for( int i = ( s ) ; i <= ( t ) ; ++ i )using namespace std ;#define N 1111vector<PII> G[N] ;int dis[N] , vis[N] ;int n , m ;queue<int>qe ;int cnt[N] ;void spfa() {    while(!qe.empty())qe.pop() ;    for (int i = 1 ; i <= n ; i ++ )dis[i] = 1 , vis[i] = 1 , qe.push(i) ;    mem(cnt ,0) ;    while(!qe.empty()) {        int tp = qe.front() ;        qe.pop() ;        vis[tp] = 0 ;        if(cnt[tp] > n) {            puts("Impossible.") ;            return ;        }        int sz = G[tp].size() ;        for (int i = 0 ; i < sz ; i ++ ) {            int e = G[tp][i].FI ;            int l = G[tp][i].SE ;            if(dis[e] < dis[tp] + l) {                dis[e] = dis[tp] + l ;                if(!vis[e]) {                    vis[e] = 1 ;                    qe.push(e) ;                    cnt[e] ++ ;                }            }        }    }    int mx = inf ;    for (int i = 1 ; i <= n ; i ++ ){        mx = min(dis[i] , mx) ;//        if(dis[i] >= 1000000){//            puts("Impossible.");return ;//        }    }    for (int i = 1 ; i <= n ; i ++ ){        dis[i] -= mx - 1 ;    }    for (int i = 1 ; i <= n ; i ++ ){        if(dis[i] >= 1000000){            puts("Impossible.") ; return ;        }    }    for (int i = 1 ; i < n ; i ++ )printf("%d ",dis[i]) ;    cout << dis[n] << endl;}char a[1111][111] ;int main() {    while(cin >> n , n) {        for (int i = 1 ; i <= n ; i ++ )G[i].clear() ;        cin >> m ;        int s , e , l ;        for (int i = 0 ; i < m ; i ++ ) {            scanf("%s %d %s %s",a[1] , &s , a[2] , a[3]) ;            if(a[3][0] == 'a'){                scanf("%s %d %s %s %s %s %d",a[1],&l ,a[1],a[1],a[1],a[1] ,&e) ;                G[e].push_back(mp(s , l)) ;            }            else {                scanf("%d %s %s %s %s %s %s %s %d",&l ,a[1] ,a[1],a[1],a[1],a[1],a[1],a[1] , &e) ;                G[e].push_back(mp(s, 0)) ;                G[s].push_back(mp(e, -l)) ;            }        }        spfa() ;    }    return 0 ;}

最短路：

#include <set>#include <map>#include <stack>#include <cmath>#include <queue>#include <cstdio>#include <string>#include <vector>#include <iomanip>#include <cstring>#include <iostream>#include <algorithm>#define Max 2505#define FI first#define SE second#define ll long long#define PI acos(-1.0)#define inf 0x3fffffff#define LL(x) ( x << 1 )#define bug puts("here")#define PII pair<int,int>#define RR(x) ( x << 1 | 1 )#define mp(a,b) make_pair(a,b)#define mem(a,b) memset(a,b,sizeof(a))#define REP(i,s,t) for( int i = ( s ) ; i <= ( t ) ; ++ i )using namespace std ;#define N 1111vector<PII> G[N] ;int dis[N] , vis[N] ;int n , m ;queue<int>qe ;int cnt[N] ;void spfa() {    while(!qe.empty())qe.pop() ;    for (int i = 1 ; i <= n ; i ++ )dis[i] = inf , vis[i] = 1 , qe.push(i) ;    mem(cnt ,0) ;    while(!qe.empty()) {        int tp = qe.front() ;        qe.pop() ;        vis[tp] = 0 ;        if(cnt[tp] > n) {            puts("Impossible.") ;            return ;        }        int sz = G[tp].size() ;        for (int i = 0 ; i < sz ; i ++ ) {            int e = G[tp][i].FI ;            int l = G[tp][i].SE ;            if(dis[e] > dis[tp] + l) {                dis[e] = dis[tp] + l ;                if(!vis[e]) {                    vis[e] = 1 ;                    qe.push(e) ;                    cnt[e] ++ ;                }            }        }    }    int mx = inf ;    for (int i = 1 ; i <= n ; i ++ ){        mx = min(dis[i] , mx) ;//        if(dis[i] >= 1000000){//            puts("Impossible.");return ;//        }    }    for (int i = 1 ; i <= n ; i ++ ){        dis[i] -= mx - 1 ;    }    for (int i = 1 ; i <= n ; i ++ ){        if(dis[i] >= 1000000){            puts("Impossible.") ; return ;        }    }    for (int i = 1 ; i < n ; i ++ )printf("%d ",dis[i]) ;    cout << dis[n] << endl;}char a[1111][111] ;int main() {    while(cin >> n , n) {        for (int i = 1 ; i <= n ; i ++ )G[i].clear() ;        cin >> m ;        int s , e , l ;        for (int i = 0 ; i < m ; i ++ ) {            scanf("%s %d %s %s",a[1] , &s , a[2] , a[3]) ;            if(a[3][0] == 'a'){                scanf("%s %d %s %s %s %s %d",a[1],&l ,a[1],a[1],a[1],a[1] ,&e) ;//                G[e].push_back(mp(s , l)) ;                G[s].push_back(mp(e , -l)) ;            }            else {                scanf("%d %s %s %s %s %s %s %s %d",&l ,a[1] ,a[1],a[1],a[1],a[1],a[1],a[1] , &e) ;//                G[e].push_back(mp(s, 0)) ;//                G[s].push_back(mp(e, -l)) ;                G[e].push_back(mp(s , l)) ;                G[s].push_back(mp(e , 0)) ;            }        }        spfa() ;    }    return 0 ;}