HDU-1534 Schedule Problem

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题目大意：

给你n个项目，并给出m个约束，其中SAF表示start after finish, SAS 表示start after start， FAS表示finish after start， FAF表示finish after finish

解题思路：

差分约束

代码：

#include <queue>#include <cstdio>#include <vector>#include <cstring>using namespace std;const int maxn = 10000 + 5;const int INF = 0x3f3f3f3f;typedef struct node{    int to, w;    node(int a = 0, int b = 0){        to = a; w = b;    }}Edge;vector<Edge> vec[maxn];int t[maxn], dis[maxn], vis[maxn], cnt[maxn];int spfa(int n){    Edge v;    int p, len;    queue<int> q;    while(!q.empty()) q.pop();    for(int i = 0; i < maxn; ++i){        vis[i] = 0; cnt[i] = 0;        dis[i] = INF;    }    q.push(0);    dis[0] = 0; vis[0] = 1; cnt[0] = 1;    while(!q.empty()){        p = q.front(); q.pop(); vis[p] = 0;        len = vec[p].size();        for(int i = 0; i < len; ++i){            v = vec[p][i];            if(dis[v.to] > dis[p] + v.w){                dis[v.to] = dis[p] + v.w;                if(!vis[v.to]){                    q.push(v.to);                    vis[v.to] = 1; cnt[v.to] += 1;                    if(cnt[v.to] >= n) return 0;                }            }        }    }    return 1;}int main(){    int a, b, n, cas = 1;    while(~scanf("%d", &n) && n){        for(int i = 1; i <= n; ++i){            scanf("%d", &t[i]);        }        for(int i = 0; i <= n; ++i) vec[i].clear();        char op[5] = {0};        while(~scanf(" %s", op)){            if(strcmp(op, "#") == 0) break;            scanf("%d%d", &a, &b);            if(strcmp(op, "FAS") == 0) vec[b].push_back(Edge(a, t[a]));            else if(strcmp(op, "FAF") == 0) vec[b].push_back(Edge(a, t[a] - t[b]));            else if(strcmp(op, "SAF") == 0) vec[b].push_back(Edge(a, -t[b]));            else vec[b].push_back(Edge(a, 0));        }        for(int i = 1; i <= n; ++i){            vec[0].push_back(Edge(i, 0));        }        printf("Case %d:\n", cas++);        if(spfa(n)){            for(int i = 1; i <= n; ++i){                printf("%d %d\n", i, -dis[i]);            }        }else puts("impossible");        puts("");    }    return 0;}

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