POJ-3249 Test for Job DAG最短路

　　题目链接：http://poj.org/problem?id=3249

　　DAG图上的最短路，记忆化搜索。

  1 //STATUS:C++_AC_2000MS_14272KB

  2 #include <functional>

  3 #include <algorithm>

  4 #include <iostream>

  5 //#include <ext/rope>

  6 #include <fstream>

  7 #include <sstream>

  8 #include <iomanip>

  9 #include <numeric>

 10 #include <cstring>

 11 #include <cassert>

 12 #include <cstdio>

 13 #include <string>

 14 #include <vector>

 15 #include <bitset>

 16 #include <queue>

 17 #include <stack>

 18 #include <cmath>

 19 #include <ctime>

 20 #include <list>

 21 #include <set>

 22 #include <map>

 23 using namespace std;

 24 //define

 25 #define pii pair<int,int>

 26 #define mem(a,b) memset(a,b,sizeof(a))

 27 #define lson l,mid,rt<<1

 28 #define rson mid+1,r,rt<<1|1

 29 #define PI acos(-1.0)

 30 //typedef

 31 typedef __int64 LL;

 32 typedef unsigned __int64 ULL;

 33 //const

 34 const int N=100010;

 35 const int INF=0x3f3f3f3f;

 36 const int MOD=100000,STA=8000010;

 37 const LL LNF=1LL<<60;

 38 const double EPS=1e-8;

 39 const double OO=1e15;

 40 const int dx[4]={-1,0,1,0};

 41 const int dy[4]={0,1,0,-1};

 42 //Daily Use ...

 43 inline int sign(double x){return (x>EPS)-(x<-EPS);}

 44 template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}

 45 template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}

 46 template<class T> inline T Min(T a,T b){return a<b?a:b;}

 47 template<class T> inline T Max(T a,T b){return a>b?a:b;}

 48 template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}

 49 template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}

 50 template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}

 51 template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}

 52 //End

 53 

 54 struct Edge{

 55     int u,v;

 56 }e[N*10];

 57 int first[N],next[N*10],val[N],cnti[N],cnto[N];

 58 LL d[N];

 59 int n,m,mt;

 60 

 61 void adde(int a,int b)

 62 {

 63     e[mt].u=a;e[mt].v=b;

 64     next[mt]=first[a];first[a]=mt++;

 65 }

 66 

 67 LL dfs(int u)

 68 {

 69     if(d[u]!=-LNF)return d[u];

 70     if(!cnto[u])return d[u]=val[u];

 71     int i;

 72     for(i=first[u];i!=-1;i=next[i]){

 73         d[u]=Max(d[u],(LL)val[u]+dfs(e[i].v));

 74     }

 75     return d[u];

 76 }

 77 

 78 int main()

 79 {

 80   //  freopen("in.txt","r",stdin);

 81     int i,j,a,b;

 82     LL ans;

 83     while(~scanf("%d%d",&n,&m))

 84     {

 85         for(i=1;i<=n;i++)

 86             scanf("%d",&val[i]);

 87         mt=0;

 88         mem(first,-1);

 89         mem(cnti,0);mem(cnto,0);

 90         for(i=1;i<=m;i++){

 91             scanf("%d%d",&a,&b);

 92             cnti[b]++,cnto[a]++;

 93             adde(a,b);

 94         }

 95 

 96         ans=-LNF;

 97         for(i=1;i<=n;i++)d[i]=-LNF;

 98         for(i=1;i<=n;i++){

 99             if(!cnti[i]){

100                 ans=Max(ans,dfs(i));

101             }

102         }

103 

104         printf("%I64d\n",ans);

105     }

106     return 0;

107 }