G-island transport-hdu 4280 (maximum flow)

Test instructions: There are N Islands, M route, each road connected to two islands, and each road has a maximum number of people, now want to know from the westernmost island to the most east of the island can have the maximum number of persons in the past (the most western and eastern Islands only one).

Analysis: Can be more obvious to see is a maximum flow problem, and the source point sinks are also given, you can use the most basic dinic solution, but note some optimization, will be tle, the following is dinic AC code =========================================================================================================== =#pragmaComment (linker, "/stack:102400000,102400000")
#include <stdio.h>
#include <string.h>
#include <queue>
#include <stack>
#include <algorithm>
#include <math.h>
usingnamespaceStd

ConstintMAXN =100005;
ConstintOO = 1e9+7;

structedge{intV, flow, next;} edge[maxn<<1];
intHEAD[MAXN], CNT;
intLAYER[MAXN];

voidInIt (intN
{
CNT =0;
memset (Head,-1,sizeof(Head));
}
voidAddedge (intUintVintFlow
{
EDGE[CNT].V = v;
Edge[cnt].flow = flow;
Edge[cnt].next = Head[u];
Head[u] = cnt++;
}
BOOLBFsintStartintEND)
{
queue<int>Q; Q.push (start);
memset (layer,0,sizeof(layer));
Layer[start] =1;

while(Q.size ())
{
intU = Q.front (); Q.pop ();

if(U = = End)returntrue;

for(intJ=head[u]; j!=-1; J=edge[j].next)
{
intv = edge[j].v;

if(Layer[v] = =false&& Edge[j].flow)
{
LAYER[V] = Layer[u] +1;
Q.push (v);
}
}
}

returnfalse;
}
intDfsintUintMaxflow,intEND)
{
if(U = = End)returnMaxflow;

intUflow =0;

for(intJ=head[u]; j!=-1; J=edge[j].next)
{
intv = edge[j].v;

if(layer[v]-1= = Layer[u] && edge[j].flow)
{
intflow = min (Maxflow-uflow, edge[j].flow);
Flow = DFS (V, Flow, End);

Edge[j].flow-= flow;
edge[j^1].flow + = flow;

Uflow + = flow;

if(Uflow = = Maxflow)
Break;
}
}

if(Uflow = =0)///optimized to prevent re-search, no optimization will time out
Layer[u] =0;

returnUflow;
}
intDinic (intStartintEnd,intN
{
intMaxflow =0;

while(BFS (start, End) = =true)
Maxflow + = DFS (start, oo, End);

returnMaxflow;
}
intMain ()
{
intT

scanf"%d", &t);

while(t--)
{
intI, N, M, X, Y, East=-oo, West=oo, start, End;

scanf"%d%d", &n, &m);

InIt (N);

for(i=1; i<=n; i++)
{
scanf"%d%d", &x, &y);

if(West > x)
{
West = x;
start = i;
}
if(East < X)
{
east = x;
End = i;
}
}

while(m--)
{
intU, V, flow;

scanf"%d%d%d", &u, &v, &flow);
Addedge (U, V, flow);
Addedge (V, U, flow);
}

printf"%d\n", Dinic (Start, End, N));
}

return0;
}View Code

G-island transport-hdu 4280 (maximum flow)