学步园

传送门：【HDU】1839 Delay Constrained Maximum Capacity Path

题目分析：二分容量下限，然后每次最短路的时候只跑容量大于等于下限的边，如果最短路长度小于等于t，调整下界，否则调整上界。是不是很简单？

代码如下：

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std ;

#define REP( i , a , b ) for ( int i = ( a ) ; i <  ( b ) ; ++ i )
#define FOR( i , a , b ) for ( int i = ( a ) ; i <= ( b ) ; ++ i )
#define REV( i , a , b ) for ( int i = ( a ) ; i >= ( b ) ; -- i )
#define travel( e , H , u ) for ( Edge* e = H[u] ; e ; e = e -> next )
#define CLR( a , x ) memset ( a , x , sizeof a )

const int MAXN = 10005 ;
const int MAXE = 100005 ;
const int INF = 0x7f7f7f7f ;

struct Edge {
	int v , c ;
	int cap ;
	Edge* next ;
} ;

struct Shortest_Path_Algorithm {
	Edge E[MAXE] , *H[MAXN] , *cur ;
	int d[MAXN] ;
	bool vis[MAXN] ;
	int Q[MAXN] , head , tail ;
	
	void init () {
		cur = E ;
		CLR ( H , 0 ) ;
	}
	
	void addedge ( int u , int v , int c , int cap ) {
		cur -> v = v ;
		cur -> c = c ;
		cur -> cap = cap ;
		cur -> next = H[u] ;
		H[u] = cur ++ ;
	}
	
	int spfa ( int s , int t , int capacity ) {
		CLR ( d , INF ) ;
		CLR ( vis , 0 ) ;
		head = tail = 0 ;
		d[s] = 0 ;
		Q[tail ++] = s ;
		while ( head != tail ) {
			int u = Q[head ++] ;
			if ( head == MAXN ) head = 0 ;
			vis[u] = 0 ;
			travel ( e , H , u ) {
				int v = e -> v ;
				if ( e -> cap >= capacity && d[v] > d[u] + e -> c ) {
					d[v] = d[u] + e -> c ;
					if ( !vis[v] ) {
						vis[v] = 1 ;
						if ( d[v] < d[Q[head]] ) {
							if ( head == 0 ) head = MAXN ;
							Q[-- head] = v ;
						} else {
							Q[tail ++] = v ;
							if ( tail == MAXN ) tail = 0 ;
						}
					}
				}
			}
		}
		return d[t] ;
	}
} G ;

void scanf ( int& x , char c = 0 ) {
	while ( ( c = getchar () ) < '0' || c > '9' ) ;
	x = c - '0' ;
	while ( ( c = getchar () ) >= '0' && c <= '9' ) x = x * 10 + c - '0' ;
}

void solve () {
	int n , m , t ;
	int l = 0 , r = INF ;
	int u , v , c , cap ;
	G.init () ;
	scanf ( n ) , scanf ( m ) , scanf ( t ) ;
	while ( m -- ) {
		scanf ( u ) , scanf ( v ) , scanf ( cap ) , scanf ( c ) ;
		G.addedge ( u , v , c , cap ) ;
		G.addedge ( v , u , c , cap ) ;
		if ( cap > r ) r = cap ;
		if ( l > cap ) l = cap ;
	}
	while ( l < r ) {
		int m = ( l + r + 1 ) >> 1 ;
		if ( G.spfa ( 1 , n , m ) <= t ) l = m ;
		else r = m - 1 ;
	}
	printf ( "%d\n" , l ) ;
}

int main () {
	int T ;
	scanf ( T ) ;
	while ( T -- ) solve () ;
	return 0 ;
}