hdu 4280 网络流 sap 点边数据很大

题意：有N个岛屿 M条无向路 每个路有一最大允许的客流量，求从最西的那个岛屿最多能运用多少乘客到最东的那个岛屿。

思路：很单纯的网络流，重点是卡时间 模板的高效性很重要啊该模板详解 参见这里  模板题就不注释了

#include <stdio.h>
#include <string.h>
#define VM 100010
#define EM 400010
const int inf = 0x3f3f3f3f;
struct E
{
int to, frm, nxt, cap;
}edge[EM];

int head[VM],e,n,m,src,des;
int dep[VM], gap[VM];

void addedge(int cu, int cv, int cw)
{
edge[e].frm = cu;
edge[e].to = cv;
edge[e].cap = cw;
edge[e].nxt = head[cu];
head[cu] = e++;
edge[e].frm = cv;
edge[e].to = cu;
edge[e].cap = 0;
edge[e].nxt = head[cv];
head[cv] = e++;
}

int que[VM];

void BFS()
{
memset(dep, -1, sizeof(dep));
memset(gap, 0, sizeof(gap));
gap[0] = 1;
int front = 0, rear = 0;
dep[des] = 0;
que[rear++] = des;
int u, v;
while (front != rear)
{
u = que[front++];
front = front%VM;
for (int i=head[u]; i!=-1; i=edge[i].nxt)
{
v = edge[i].to;
if (edge[i].cap != 0 || dep[v] != -1)
continue;
que[rear++] = v;
rear = rear % VM;
++gap[dep[v] = dep[u] + 1];
}
}
}
int cur[VM],stack[VM];
int Sap()       //sap模板
{
int res = 0;
BFS();
int top = 0;
memcpy(cur, head, sizeof(head));
int u = src, i;
while (dep[src] < n)
{
if (u == des)
{
int temp = inf, inser = n;
for (i=0; i!=top; ++i)
if (temp > edge[stack[i]].cap)
{
temp = edge[stack[i]].cap;
inser = i;
}
for (i=0; i!=top; ++i)
{
edge[stack[i]].cap -= temp;
edge[stack[i]^1].cap += temp;
}
res += temp;
top = inser;
u = edge[stack[top]].frm;
}

if (u != des && gap[dep[u] -1] == 0)
break;
for (i = cur[u]; i != -1; i = edge[i].nxt)
if (edge[i].cap != 0 && dep[u] == dep[edge[i].to] + 1)
break;

if (i != -1)
{
cur[u] = i;
stack[top++] = i;
u = edge[i].to;
}
else
{
int min = n;
for (i = head[u]; i != -1; i = edge[i].nxt)
{
if (edge[i].cap == 0)
continue;
if (min > dep[edge[i].to])
{
min = dep[edge[i].to];
cur[u] = i;
}
}
--gap[dep[u]];
++gap[dep[u] = min + 1];
if (u != src)
u = edge[stack[--top]].frm;
}
}
return res;
}

int main()
{
int T, i;
scanf("%d", &T);
while (T--)
{
scanf("%d%d", &n, &m);
int x, y;
int Min = inf, Max = -inf;
for (i=1; i<=n; ++i)       //找出起点src 终点des
{
scanf("%d%d", &x, &y);
if (x <= Min)
{
src = i;
Min = x;
}
if (x >= Max)
{
des = i;
Max = x;
}
}
e = 0;
memset(head, -1, sizeof(head));
int u, v, c;
for (i=0; i!=m; ++i)
{
scanf("%d%d%d", &u, &v, &c);
addedge(u,v,c);
addedge(v,u,c);
}
int ans = Sap();
printf("%d\n", ans);
}
return 0;
}