poj1273

赤裸裸的最大流

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;

#define maxn 205
#define maxm 205
#define inf (1 << 30)

struct Edge
{
    int next, v, f;
} edge[maxm * 2];

int n, m;
int head[maxn];
int q[maxn];
bool vis[maxn];
int cur[maxn];
int dep[maxn];
int ncount;
int path[maxn];

void addedge(int a, int b, int f)
{
    edge[ncount].v = b;
    edge[ncount].f = f;
    edge[ncount].next = head[a];
    head[a] = ncount++;
}

void input()
{
    ncount = 0;
    memset(head, -1, sizeof(head));
    for (int i = 0; i < m; i++)
    {
        int a, b, f;
        scanf("%d%d%d", &a, &b, &f);
        a--;
        b--;
        addedge(a, b, f);
        addedge(b, a, 0);
    }
}

void bfs(int s, int t)
{
    memset(vis, 0, sizeof(vis));
    memset(dep, -1, sizeof(dep));
    int front = 0, rear = 0;
    q[rear++] = s;
    vis[s] = true;
    dep[s] = 0;
    while (front != rear && !vis[t])
    {
        int u = q[front++];
        for (int i = head[u]; ~i; i = edge[i].next)
        {
            int v = edge[i].v;
            if (!vis[v] && edge[i].f > 0)
            {
                q[rear++] = v;
                vis[v] = true;
                dep[v] = dep[u] + 1;
            }
        }
    }
}

int dinic(int s, int t)
{
    int ret = 0;
    while (true)
    {
        bfs(s, t);
        if (dep[t] == -1)
            break;
        int path_n = 0;
        int x = s;
        memcpy(cur, head, sizeof(cur));
        while (true)
        {
            if (x == t)
            {
                int mink = -1, delta = inf;
                for (int i = 0; i < path_n; ++i)
                {
                    if (edge[path[i]].f < delta)
                    {
                        delta = edge[path[i]].f;
                        mink = i;
                    }
                }
                for (int i = 0; i < path_n; ++i)
                {
                    edge[path[i]].f -= delta;
                    edge[path[i] ^ 1].f += delta;
                }
                ret += delta;
                path_n = mink;
                if (path_n)
                    x = edge[path[path_n - 1]].v;
                else
                    x = s;
            }
            int e;
            for (e = cur[x]; ~e; e = edge[e].next)
            {
                if (edge[e].f == 0)
                    continue;
                int y = edge[e].v;
                if (dep[x] + 1 == dep[y])
                    break;
            }
            cur[x] = e;
            if (~e)
            {
                path[path_n++] = e;
                x = edge[e].v;
            }
            else
            {
                if (path_n == 0)
                    break;
                dep[x] = -1;
                --path_n;
                if (path_n)
                    x = edge[path[path_n - 1]].v;
                else
                    x = s;
            }
        }
    }
    return ret;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    while (~scanf("%d%d", &m, &n))
    {
        input();
        printf("%d
", dinic(0, n - 1));
    }
    return 0;
}