POJ 1637 Sightseeing tour(混合图的欧拉回路）

题目链接

建个图，套个模板。

#include <cstdio>

#include <cstring>

#include <iostream>

#include <map>

#include <algorithm>

#include <vector>

#include <string>

#include <queue>

using namespace std;

#define INF 0x3ffffff

struct node

{

    int u,v,next,re,w;

}edge[20001];

int first[2001],dis[2001];

int in[2001],out[2001];

int t,str,end;

void CL()

{

    t = 1;

    memset(first,-1,sizeof(first));

}

void add(int u,int v,int w)

{

    edge[t].u = u;

    edge[t].v = v;

    edge[t].w = w;

    edge[t].re = t + 1;

    edge[t].next = first[u];

    first[u] = t ++;

    edge[t].u = v;

    edge[t].v = u;

    edge[t].w = 0;

    edge[t].re = t - 1;

    edge[t].next = first[v];

    first[v] = t ++;

}

int bfs()

{

    int u,v,i;

    memset(dis,-1,sizeof(dis));

    queue<int> que;

    que.push(str);

    dis[str] = 0;

    while(!que.empty())

    {

        u = que.front();

        que.pop();

        for(i = first[u];i != -1;i = edge[i].next)

        {

            v = edge[i].v;

            if(edge[i].w > 0&&dis[v] < 0)

            {

                dis[v] = dis[u] + 1;

                que.push(v);

            }

        }

    }

    if(dis[end] > 0) return 1;

    else return 0;

}

int dfs(int u,int step)

{

    int i,temp,v,tf = 0;

    if(u == end) return step;

    for(i = first[u];i != -1;i = edge[i].next)

    {

        v = edge[i].v;

        if(edge[i].w > 0&&dis[v] == dis[u] + 1&&(temp = dfs(v,min(step,edge[i].w))))

        {

            edge[i].w -= temp;

            edge[edge[i].re].w += temp;

            return temp;

        }

    }

    if(!tf) dis[u] = -1;

    return tf;

}

int main()

{

    int t,i,u,v,k,n,m;

    scanf("%d",&t);

    while(t--)

    {

        memset(in,0,sizeof(in));

        memset(out,0,sizeof(out));

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

        CL();

        str = 0;

        end = n + 1;

        for(i = 0;i < m;i ++)

        {

            scanf("%d%d%d",&u,&v,&k);

            in[u] ++;

            out[v] ++;

            if(k != 1)

            add(u,v,1);

        }

        for(i = 1;i <= n;i ++)

        {

            if(abs(in[i]-out[i])%2 == 1)

            break;

        }

        if(i != n+1)

        {

            printf("impossible\n");

            continue;

        }

        int sum = 0;

        for(i = 1;i <= n;i ++)

        {

            if(in[i] > out[i])

            {

                add(str,i,(in[i]-out[i])/2);

                sum += (in[i]-out[i])/2;

            }

            else

            {

                add(i,end,(out[i]-in[i])/2);

            }

        }

        int ans = 0,res;

        while(bfs())

        {

            while(res = dfs(str,INF))

            ans += res;

        }

        if(ans == sum)

        printf("possible\n");

        else

        printf("impossible\n");

    }

    return 0;

}

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