http://poj.org/problem?id=1201
设si[i+1]表示有不超过i的Z集合里面的数的个数，可以列出不等式si[b+1]-si[a]>=ci
另有隐含条件 si[i+1]-s[i]>=0 si[i]-s[i+1]>=-1 利用spfa求出最长路
View Code
1 #include <iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<stdlib.h> 5 #include<queue> 6 using namespace std; 7 #define IN 50010 8 #define INF 0x3f3f3f 9 struct node 10 { 11 int u,v,w,next; 12 }men[IN*4]; 13 int t,first[IN],n,dis[IN],vis[IN]; 14 void init() 15 { 16 t = 0; 17 memset(first,-1,sizeof(first)); 18 } 19 void add(int u,int v,int w) 20 { 21 men[t].u = u; 22 men[t].v = v; 23 men[t].w = w; 24 men[t].next = first[u]; 25 first[u] = t; 26 t++; 27 } 28 void spfa(int st) 29 { 30 int i; 31 for(i = 0; i <= n ; i++) 32 dis[i] = -INF; 33 queue<int>q; 34 q.push(st); 35 memset(vis,0,sizeof(vis)); 36 vis[st] = 1; 37 dis[st] = 0; 38 while(!q.empty()) 39 { 40 int u = q.front(); 41 vis[u] = 0; 42 q.pop(); 43 for(i = first[u];i!=-1 ; i = men[i].next) 44 { 45 int v = men[i].v; 46 int w = men[i].w; 47 if(dis[v]<dis[u]+w) 48 { 49 dis[v] = dis[u]+w; 50 if(!vis[v]) 51 { 52 vis[v] = 1; 53 q.push(v); 54 } 55 } 56 } 57 } 58 } 59 int main() 60 { 61 int i,a,b,c,ma=-1,mi = IN; 62 while(cin>>n) 63 { 64 init(); 65 for(i = 1; i <= n ; i++) 66 { 67 cin>>a>>b>>c; 68 add(a,b+1,c); 69 if(b+1>ma) 70 ma = b+1; 71 if(a<mi) 72 mi = a; 73 } 74 for(i = mi ; i <= ma ; i++) 75 { 76 add(i,i+1,0); 77 add(i+1,i,-1); 78 } 79 spfa(mi); 80 cout<<dis[ma]<<endl; 81 } 82 return 0; 83 }