pku 1275 Cashier Employment 差分约束

http://poj.org/problem?id=1275

题意：http://972169909-qq-com.iteye.com/blog/1185527 这个解题报告描述的相当详细了。就不多说了;

差分约束关键是找出约束条件，然后建图。最后就是套spfa或者bellman_ford的模板就是了;

#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
#define maxn 25
using namespace std;

struct node
{
    int v,w;
    int next;
}g[10*maxn];
int cnt,pre[maxn],ind[maxn],dis[maxn];
bool inq[maxn];
int R[maxn],num[26];
const int inf = 9999999;

void init()
{
    cnt = 0;
    memset(pre,-1,sizeof(pre));
    memset(ind,0,sizeof(ind));
    memset(inq,false,sizeof(inq));
}
void add(int u,int v,int w)
{
    g[cnt].v = v;
    g[cnt].w = w;
    g[cnt].next = pre[u];
    pre[u] = cnt++;
}
bool spfa(int s)
{
    int i;
    queue<int>q;
    for (i = 0; i < maxn; ++i) dis[i] = -inf;
    dis[s] = 0;
    q.push(s); inq[s] = true;
    while (!q.empty())
    {
        int u = q.front(); q.pop();
        if (++ind[u] > 24) return false;
        inq[u] = false;
        for (i = pre[u]; i != -1; i = g[i].next)
        {
            int v = g[i].v, w = g[i].w;
            if (dis[v] < dis[u] + w)
            {
                dis[v] = dis[u] + w;
                if (!inq[v])
                {
                    inq[v] = true;
                    q.push(v);
                }
            }
        }
    }
    return true;
}
int main()
{
    int i,t,pos,n;
    scanf("%d",&t);
    while (t--)
    {
        memset(num,0,sizeof(num));
        for (i = 1; i <= 24; ++i) scanf("%d",&R[i]);
        scanf("%d",&n);
        for (i = 0; i < n; ++i)
        {
            scanf("%d",&pos);
            num[pos + 1]++;
        }
        int l = 0, r = n;
        bool flag = false;
        while (l < r)
        {
            init();
            int mid = (l + r)>>1;
            for (i = 1; i <= 24; ++i)
            {
                add(i - 1,i,0);
                add(i,i - 1,-num[i]);
            }
            for (i = 8; i <= 24; ++i)
            add(i - 8,i,R[i]);
            for (i = 1; i <= 7; ++i)
            add(i + 16,i,R[i] - mid);
            add(0,24,mid);
            if (spfa(0))
            {
                r = mid;
                flag = true;
            }
            else
            {
                l = mid + 1;
            }
        }
        if (flag) printf("%d\n",r);
        else printf("No Solution\n");
    }
    return 0;
}