[题解]「最短路,Noip2009」最优贸易

  1 #include <iostream>
  2 #include <cstdio>
  3 #include <algorithm>
  4 #include <cstring>
  5 #include <queue> 
  6 #define Inf 0x7fffff
  7 const int Maxx = 500000;
  8  
  9 using namespace std;
 10  
 11 int Head[2*Maxx+1] , Next[2*Maxx+1] , Value[Maxx+1];
 12 int Heads[2*Maxx+1] , Nexts[2*Maxx+1];
 13 int F[Maxx+1] , D[Maxx+1] , T1[Maxx+1] , T2[Maxx+1];
 14 int N , M , Sum = 0 , Num = 0 , X , Y , Z;
 15 struct Yuns{
 16     int X;
 17     int Y;
 18 }Ver[2*Maxx+1];
 19 struct Yunss{
 20     int X;
 21     int Y;
 22 }Vers[2*Maxx+1];
 23 priority_queue < pair<int , int> > Q1;
 24 priority_queue < pair<int , int> > Q2;
 25  
 26 int Read(){
 27     
 28     int x = 0;
 29     char c = getchar();
 30     while(c < ‘0‘ || c > ‘9‘) c = getchar();
 31     while(c >= ‘0‘ && c <= ‘9‘) x = x*10 + c-‘0‘ , c = getchar();
 32     return x;
 33  
 34 }
 35  
 36 void Add(int X , int Y){
 37     Ver[++Sum].X = X;
 38     Ver[Sum].Y = Y;
 39     Next[Sum] = Head[X];
 40     Head[X] = Sum;
 41     return;
 42 }
 43  
 44 void Add_T(int X , int Y){
 45     Vers[++Num].X = X;
 46     Vers[Num].Y = Y;
 47     Nexts[Num] = Heads[X];
 48     Heads[X] = Num;
 49     return;
 50 }
 51  
 52 void Dijkstra_1(){
 53     F[1] = Value[1];
 54     Q1.push(make_pair(F[1] , 1));
 55     while(Q1.size()){
 56         int Tag = Q1.top().second;
 57         Q1.pop();
 58         if (T1[Tag]) continue;
 59         T1[Tag] = 1;
 60         for (int i = Head[Tag] ; i ; i = Next[i]){
 61             int Y = Ver[i].Y;
 62             F[Y] = min(F[Tag] , Value[Y]);
 63             Q1.push(make_pair(F[Y] , Y));
 64         } 
 65     }
 66     return;
 67 }
 68  
 69 void Dijkstra_2(){
 70     D[N] = Value[N];
 71     Q2.push(make_pair(D[N] , N));
 72     while(Q2.size()){
 73         int Tag = Q2.top().second;
 74         Q2.pop();
 75         if (T2[Tag]) continue;
 76         T2[Tag] = 1;
 77         for (int i = Heads[Tag] ; i ; i = Nexts[i]){
 78             int Y = Vers[i].Y;
 79             D[Y] = max(D[Tag] , Value[Y]);
 80             Q2.push(make_pair(D[Y] , Y));     
 81         } 
 82     }
 83     return;
 84 }
 85  
 86 void In_Work(){
 87     
 88     cin >> N >> M;
 89     for (int i = 1 ; i <= N ; i++) Value[i] = Read(); 
 90     for (int i = 1 ; i <= M ; i++){
 91         X = Read() , Y = Read() , Z = Read();
 92         Add(X , Y);
 93         Add_T(Y , X);
 94         if (Z == 2) Add(Y , X) , Add_T(X , Y);
 95     }
 96     
 97     for(int i = 1 ; i <= N ; i++) F[i] = Inf;
 98     for(int i = 1 ; i <= N ; i++) D[i] = Inf;
 99     Dijkstra_1();
100     Dijkstra_2();
101     
102 }
103  
104 void In_Out(){
105     
106     int Ans = -1; 
107     for(int i = 1 ; i <= N ; i++)
108         if (D[i]!=Inf && F[i]!=Inf)
109             Ans = max(Ans , D[i]-F[i]);
110     cout << Ans;
111     
112 } 
113 void In_File(){
114 //    freopen("dance.in" , "r" , stdin);
115 //    freopen("dance.out" , "w" , stdout);
116 }
117  
118 int main(){
119     
120     In_File();
121     
122     In_Work();
123     
124     In_Out();
125     
126     return 0;    
127     
128 }