poj-1752 Advertisement **

  1 /*
  2  * 很自然的 差分约束系统， 没具体写， 转一个。。
  3  * 
  4  *
  5  *　　http://www.cnblogs.com/ihainan/archive/2011/07/23/2114884.html
  6  * 解题思路：由题可得如下约束条件:
  7  *　　如果 b - a >= k 
  8  *       则 S[b] - S[a] >= k
  9  *　　 否则  S[b] - S[a] >= dis(a, b)  
 10  *            且 S[b] - S[a] <= dis(a, b)
 11  *　　同时 0 <= S[i]  - S[i - 1] <= 1
 12  *
 13  *   由约束条件可建图，spfa求最长路
 14  *
 15  *     STL里面的东西最好还是不用，写出来的spfa甚至比bellman还慢！！！
 16  */
 17 
 18 #include<stdio.h>
 19 #include<string.h>
 20 #define N 1200
 21 #define maxint 0xfffffff
 22 #define num 40000
 23 void init(), spfa(),  print(), addedge(int, int, int);
 24 struct EDGE{
 25     int x, y, w, next;
 26 }e[5 * num];
 27 int head[3 * num], n, k, m = 0, dis[3 * num], vis[3 * num], ans = 0, minnum = maxint, maxnum = -maxint, queue[num * 300];
 28 int main()
 29 {
 30     init();
 31     spfa();
 32     print();
 33     return 0;
 34 }
 35 void init()
 36 {
 37     int i, j, a, b, c, ch;
 38     memset(head, -1, sizeof(head));
 39     memset(dis, 0, sizeof(dis));
 40     scanf("%d %d", &k, &n);
 41     for(i = 1; i <= n; ++i){
 42         scanf("%d %d", &a, &b);
 43         if(a > b){
 44             ch = a;
 45             a = b;
 46             b = ch;
 47         }
 48         a += num - 1;
 49         b += num;
 50         minnum = minnum < a ? minnum : a;
 51         maxnum = maxnum > b ? maxnum : b;
 52         c = b - a;
 53         if(c < k){
 54             addedge(a, b, c);
 55             addedge(b, a, -c);
 56         }
 57         else
 58             addedge(a, b, k);
 59     }
 60 }
 61 void addedge(int x, int y, int w)
 62 {
 63     ++m;
 64     e[m].x = x;
 65     e[m].y = y;
 66     e[m].w = w;
 67     e[m].next = head[x];
 68     head[x] = m;
 69 }
 70  
 71 void spfa()
 72 {
 73     int i, j, x, y, tail = 0, front = 0;
 74     for(i = minnum; i <= maxnum; ++i){
 75         if(i != 0){
 76             queue[++tail] = i;
 77             addedge(i, i + 1, 0);
 78             addedge(i + 1, i, -1);
 79         }
 80         dis[i] = -maxint;
 81         vis[i] = 0;
 82     }
 83     dis[minnum] = 0;
 84     vis[minnum] = 1;
 85     while(front < tail){
 86         x = queue[++front];
 87         vis[x] = 0;
 88         for(i = head[x]; i != -1; i = e[i].next){
 89             y = e[i].y;
 90             if(dis[x] + e[i].w > dis[y]){
 91                 dis[y] = e[i].w + dis[x];
 92                 if(!vis[y]){
 93                     vis[y] = 1;
 94                     queue[++tail] = y;
 95                 }
 96             }
 97         }
 98     }
 99 }
100  
101 void print()
102 {
103     int i;
104     printf("%d\n", dis[maxnum]);
105     for(i = minnum; i <= maxnum; ++i)
106         if(dis[i] - dis[i - 1] == 1 )
107             printf("%d\n", i - num);
108 }