UVA 11280 Flying to Fredericton

用spfa做的时候 标记每个点的被松弛的次数 即可。

#include <iostream>
#include <vector>
#include <cstring>
#include <queue>
#include <string>
#include <map>
#include <cstdio>
#define maxn 110
#define INF 1 << 30
using namespace std;
typedef pair<int,int> pii;
vector<int> v,next,w;
int first[maxn],e;
int inq[maxn][maxn],d[maxn][maxn];

inline int min(int a,int b)
{
    return a < b ? a : b;
}

void init()
{
    v.clear();
    next.clear();
    w.clear();
    memset(first,-1,sizeof(first));
    e = 0;
}

void add_edge(int a,int b,int c)
{
    v.push_back(b);
    next.push_back(first[a]);
    first[a] = e;
    w.push_back(c);
    e++;
}

void spfa(int start,int end,int n,int len)
{
    if(len > maxn - 1)  len = maxn - 1;//这里太淫荡了。。
    queue <pii> q;
    for(int i = 0;i <= len;i++)
        for(int j = 0;j <= n;j++)
        {
            inq[i][j] = 0;
            d[i][j] = INF;
        }

    d[0][start] = 0;
    inq[0][start] = 1;
    q.push(make_pair(0,start));

    while(!q.empty())
    {
        int times = q.front().first;
        int u = q.front().second;
        //printf("current times = %d,current point = %d\n",times,u);
        inq[times][u] = 0;
        q.pop();

        for(int i = first[u];i != -1;i = next[i])
        {
            if(times + 1 <= len && d[times + 1][v[i]] > d[times][u] + w[i])
            {
                //printf("succeed:times = %d,point = %d,dist = %d\n",times,v[i],d[times][u] + w[i]);
                d[times + 1][v[i]] = d[times][u] + w[i];
                if(!inq[times + 1][v[i]])
                {
                    inq[times + 1][v[i]] = 1;
                    q.push(make_pair(times + 1,v[i]));
                }
            }
        }
    }

    int ans = INF;
    for(int t = 0;t <= len;t++)
        ans = ans < d[t][end] ? ans : d[t][end];

    if(ans == INF)  printf("No satisfactory flights\n");
    else            printf("Total cost of flight(s) is $%d\n",ans);
}

int main()
{
    int T;
    scanf("%d",&T);
    for(int kase = 1;kase <= T;kase++)
    {
        map<string,int> m;
        int start,end;
        int n,M;
        scanf("%d",&n);
        for(int i = 0;i < n;i++)
        {
            string str;
            cin>>str;
            m[str] = i;
            if(str == "Calgary")    start = i;
            else if(str == "Fredericton")    end = i;
        }
        //printf("start = %d,end = %d\n",start,end);
        init();
        scanf("%d",&M);
        for(int i = 0;i < M;i++)
        {
            int cost;
            string str1,str2;
            cin>>str1>>str2>>cost;
            add_edge(m[str1],m[str2],cost);
        }

        if(kase > 1)    printf("\n");
        printf("Scenario #%d\n",kase);
        int q,len;
        scanf("%d",&q);
        while(q--)
        {
            scanf("%d",&len);
            spfa(start,end,n,len + 1);
        }

    }
    return 0;
}