洛谷P1462 通往奥格瑞玛的道路 二分答案+最短路SPFA

 1 #include <bits/stdc++.h> 
 2 #define LL long long 
 3 #define For(i,j,k) for(int i=j;i<=k;i++) 
 4 using namespace std ; 
 5 
 6 const int N = 10011 , M = 50011 ; 
 7 struct node{
 8     LL to,pre,val ; 
 9 }e[M*2];
10 struct edge{
11     LL x,y,val ; 
12 }beg[M];
13 LL n,m,b,cnt,point[N],head[N],mx,blood,dist[N] ;
14 bool visit[N] ;  
15 queue<LL> Q ; 
16 
17 inline LL read() 
18 {
19     LL x = 0 , f = 1 ; 
20     char ch = getchar() ; 
21     while(ch<‘0‘||ch>‘9‘) { if(ch==‘-‘) f = -1 ; ch = getchar() ; } 
22     while(ch>=‘0‘&&ch<=‘9‘) { x = x * 10+ch-48 ; ch = getchar() ; } 
23     return x * f ; 
24 }
25 
26 inline void add(int x,int y,int val) 
27 {
28     e[cnt].to = y ; 
29     e[cnt].pre = head[x] ; 
30     e[cnt].val = val ; 
31     head[x] = cnt++ ; 
32 }
33 
34 inline bool check( int mid ) 
35 {
36     LL u,v ; 
37     For(i,0,n) head[i] = -1,dist[i] = (1LL<<62) ; 
38     cnt = 0 ; 
39     For(i,1,m) {
40         if( point[beg[ i ].x] > mid ) continue ; 
41         if( point[beg[ i ].y] > mid ) continue ; 
42         add( beg[ i ].x,beg[ i ].y,beg[ i ].val ) ; 
43         add( beg[ i ].y,beg[ i ].x,beg[ i ].val ) ; 
44     }
45     while(!Q.empty()) Q.pop() ; 
46     Q.push(1) ; dist[ 1 ] = 0 ; visit[ 1 ] = 1 ;  
47     while(!Q.empty()) {
48         u = Q.front() ;
49         Q.pop() ;  
50         visit[u] = 0 ; 
51         for(int i=head[u];~i;i=e[i].pre) {
52             v = e[ i ].to ; 
53             if( dist[ u ] +  e[ i ].val < dist[ v ] ) {
54                 dist[ v ] = dist[ u ] + e[ i ].val ;   
55                 if( !visit[ v ] ) {
56                     visit[ v ] = 1 ; 
57                     Q.push(v) ; 
58                 }
59             }
60         }
61     }
62     if( dist[n]>=blood || dist[n]==dist[0] ) return 0 ;   // 血量不够 或者 不能到达  
63     return 1 ;  
64 }
65 
66 inline void erfen() 
67 {
68     LL l = 0 , r = mx+1,mid ; 
69     while( l < r ) {
70         mid = ( l+r )/2 ; 
71         if( check( mid ) ) 
72             r = mid ; 
73         else 
74             l = mid+1 ;  
75     } 
76     if(r==mx+1) {
77         printf("AFK\n") ;
78         exit(0) ;  
79     }
80     printf("%d\n",r) ; 
81 }
82 
83 int main() 
84 {
85     n = read() ; m = read() ; blood = read() ; 
86     For(i,1,n) point[ i ] = read(),mx = max(mx,point[ i ]) ;  
87     For(i,1,m) {
88         beg[ i ].x = read() ; beg[ i ].y = read() ; beg[ i ].val = read() ; 
89     }
90     erfen() ; 
91     return 0 ; 
92 }