Hdu 4280 最大流<模板>.cpp

题意：

给了一个T 代表有 T 组数据

每组数据给出 n 个点和 m 条边

然后接下来 n 行..x, y 表示每个点的坐标

然后 m 行..a b w 表示 a 点和 b 点之间有权值 w..

求最大流..

思路：

主要是最大流的方法..

最大流ISAP，邻接表+GAP+当前弧优化

Tips：

理解用法..

Code：

#include <stdio.h>
#include <cstring>
#include <iostream>
using namespace std;
#define clr(x) memset(x, 0xff, sizeof(x))
#define min(a,b)(a)<(b)?(a):(b)

const int INF = 0x1f1f1f1f;
const int maxn = 100010;
const int maxm = 200010;
struct Edge
{
    int from;
    int to;
    int next;
    int w;
}edge[maxm];
int tot;
int head[maxn];

void add(int s, int u, int w)
{
    edge[tot].from = s;
    edge[tot].to = u;
    edge[tot].w = w;
    edge[tot].next = head[s];
    head[s] = tot++;
    edge[tot].from = u;
    edge[tot].to = s;
    edge[tot].w = w;
    edge[tot].next = head[u];
    head[u] = tot++;
}

int q[maxn];
int cnt[maxn];
int d[maxn];
int low[maxn];
int cur[maxn];

int maxflow(int s, int t, int n)
{
    int *front = q, *rear = q;
    for(int i = 1; i <= n; ++i) {
        d[i] = n;
        cnt[i] = 0;
    }
    cnt[n] = n-1;
    cnt[0]++;
    d[t] = 0;
    *rear++ = t;
    while(front < rear) {
        int v = *front++;
        for(int i = head[v]; i != -1; i = edge[i].next) {
            if(d[edge[i].to] == n && edge[i^1].w > 0) {
                d[edge[i].to] = d[v] + 1;
                cnt[n]--;
                cnt[d[edge[i].to]]++;
                *rear++ = edge[i].to;
            }
        }
    }

    int flow = 0, u = s, top = 0;
    low[0] = INF;
    for(int i = 1; i <= n; ++i) {
        cur[i] = head[i];
    }
    while(d[s] < n) {
        int &i = cur[u];
        for(; i != -1; i = edge[i].next) {
            if(edge[i].w > 0 && d[u] == d[edge[i].to]+1) {
                low[top+1] = min(low[top], edge[i].w);
                q[++top] = i;
                u = edge[i].to;
                break;
            }
        }
        if(i != -1) {
            if(u == t) {
                int minf = low[top];
                for(int p = 1, i; p <= top; ++p) {
                    i = q[p];
                    edge[i].w -= minf;
                    edge[i^1].w += minf;
                }
                flow += minf;
                u = s;
                low[0] = INF;
                top = 0;
            }
        }
        else {
            int old_du = d[u];
            cnt[old_du]--;
            d[u] = n-1;
            for(int i = head[u]; i != -1; i = edge[i].next)
                if(edge[i].w > 0 && d[u] > d[edge[i].to]) {
                    d[u] = d[edge[i].to];
                }
                cnt[++d[u]]++;
                if(d[u]<n)
                    cur[u] = head[u];
                if(u != s) {
                    u = edge[q[top]].from;
                    --top;
                }
                if(cnt[old_du] == 0) break;
        }
    }
    return flow;
}

struct Node
{
    int x;
    int y;
}node[100010];

int main()
{
    int i, j, k;
    int T, n, m;
    int a, b, c;
    int start, end;
    while(scanf("%d", &T) != EOF)
    while(T--)
    {
        start = end = 1;
        tot = 0;
        clr(head);

        scanf("%d %d", &n, &m);
        for(i = 1; i <= n; ++i) {
            scanf("%d %d", &node[i].x, &node[i].y);
            if(node[i].x > node[end].x) {
                end = i;
            }
            if(node[i].x < node[start].x) {
                start = i;
            }
        }

        while(m--) {
            scanf("%d %d %d", &a, &b, &c);
            add(a, b, c);
        }

        int ans = maxflow(start, end, n);
        printf("%d\n", ans);
    }
    return 0;
}

题目连接：http://acm.hdu.edu.cn/showproblem.php?pid=4280