P1343 地震逃生【最大流_EK算法+Dinic解】

模板题哒哒哒！

这题怎么判的那么慢，等了好几分钟，结果RE！我？？？……看了眼题面，零流的时候要特判，不然除数为0了啊QAQ

EK解~

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#define INF 0x3f3f3f3f
using namespace std;

inline int read()
{
    int x = 0, f = 1; char c = getchar();
    while(c < '0' || c > '9') { if(c == '-') f = -f; c = getchar(); }
    while(c >= '0' && c <= '9') { x = x * 10 + c - '0'; c = getchar(); }
    return x * f;
}

const int maxN = 202;
const int maxM = 2003;

int n, m, s, t, x;

struct EDGE{
    int adj, to, w;
    EDGE(int a = -1, int b = 0, int c = 0): adj(a), to(b), w(c) {}
}edge[maxM << 1];
int head[maxN], cnt;

void add_edge(int u, int v, int w)
{
    edge[cnt] = EDGE(head[u], v, w);
    head[u] = cnt ++ ;
}

struct Pre{
    int last, Eid;
}pre[maxN];
bool visited[maxN];

void update_residual_network(int u, int flow)
{
    while(~pre[u].last)
    {
        edge[pre[u].Eid].w -= flow;
        edge[pre[u].Eid ^ 1].w += flow;
        u = pre[u].last;
    }
}

bool find_path_bfs()
{
    memset(visited, false, sizeof(visited));
    memset(pre, -1, sizeof(pre));
    queue<int>q;
    q.push(s); visited[s] = true;
    while(!q.empty())
    {
        int u = q.front(); q.pop();
        for(int i = head[u]; ~i; i = edge[i].adj)
        {
            int v = edge[i].to;
            if(!visited[v] && edge[i].w)
            {
                pre[v] = Pre{u, i};
                if(v == t) return true;
                q.push(v); visited[v] = true;
            }
        }
    }
    return false;
}

int EK_maxFlow()
{
    int maxFlow = 0;
    while(find_path_bfs())
    {
        int newFlow = INF;
        for(int i = t; i != s; i = pre[i].last)
            newFlow = min(newFlow, edge[pre[i].Eid].w);
        update_residual_network(t, newFlow);
        maxFlow += newFlow;
    }
    return maxFlow;
}

int main()
{
    memset(head, -1, sizeof(head));

    n = read(); m = read(); x = read();
    s = 1; t = n;
    for(int i = 0; i < m; ++ i)
    {
        int u, v, w;
        u = read(); v = read(); w = read();
        add_edge(u, v, w);
        add_edge(v, u, 0);
    }
    int mx = EK_maxFlow();
    if(!mx)
        printf("Orz Ni Jinan Saint Cow!");
    else
    {
        int num = x / mx + (x % mx ? 1 : 0);
        printf("%d %d\n", mx, num);
    }
    return 0;
}

Dinic解~

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#define INF 0x3f3f3f3f
using namespace std;

inline int read()
{
    int x = 0, f = 1; char c = getchar();
    while(c < '0' || c > '9') { if(c == '-') f = -f; c = getchar(); }
    while(c >= '0' && c <= '9') { x = x * 10 + c - '0'; c = getchar(); }
    return x * f;
}

const int maxN = 202;
const int maxM = 2003;

int n, m, s, t, x;

struct EDGE{
    int adj, to, w;
    EDGE(int a = -1, int b = 0, int c = 0): adj(a), to(b), w(c) {}
}edge[maxM << 1];
int head[maxN], cnt;

void add_edge(int u, int v, int w)
{
    edge[cnt] = EDGE(head[u], v, w);
    head[u] = cnt ++;
}

int deep[maxN];

bool bfs()
{
    memset(deep, 0, sizeof(deep));
    queue<int>q;
    q.push(s); deep[s] = 1;
    while(!q.empty())
    {
        int u = q.front(); q.pop();
        for(int i = head[u]; ~i; i = edge[i].adj)
        {
            int v = edge[i].to;
            if(!deep[v] && edge[i].w)
            {
                deep[v] = deep[u] + 1;
                q.push(v);
            }
        }
    }
    return deep[t];
}

int dfs(int u, int flow)
{
    if(u == t) return flow;
    for(int i = head[u]; ~i; i = edge[i].adj)
    {
        int v = edge[i].to;
        if(deep[v] == deep[u] + 1 && edge[i].w)
        {
            if(int newFlow = dfs(v, min(flow, edge[i].w)))
            {
                edge[i].w -= newFlow;
                edge[i ^ 1].w += newFlow;
                return newFlow;
            }
        }
    }
    return 0;
}

int dinic()
{
    int maxFlow = 0;
    while(bfs())
    {
        if(int newFlow = dfs(s, INF))
            maxFlow += newFlow;
    }
    return maxFlow;
}

int main()
{
    memset(head, -1, sizeof(head));

    n = read(); m = read(); x = read();
    s = 1; t = n;
    for(int i = 0; i < m; ++ i )
    {
        int u, v, w;
        u = read(); v = read(); w = read();
        add_edge(u, v, w);
        add_edge(v, u, 0);
    }
    int mx = dinic();
    if(!mx)
        printf("Orz Ni Jinan Saint Cow!\n");
    else
    {
        int num = x / mx + (x % mx ? 1 : 0);
        printf("%d %d\n", mx, num);
    }
    return 0;
}