POJ 1637 Sightseeing tour 混合图欧拉回路 最大流

题目大意：给出一张混合图，问是否存在欧拉回路。 

思路：成题，直接看题解吧。

http://www.cnblogs.com/Lyush/archive/2013/05/01/3052847.html

CODE:

#include <queue>#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>#define MAX 510#define MAXE 5000000#define INF 0x3f3f3f3f#define S 0#define T (MAX - 1)using namespace std;#define min(a,b) ((a) < (b) ? (a):(b))#define max(a,b) ((a) > (b) ? (a):(b))struct Edge{int x,y;bool directed;void Read() {int z;scanf("%d%d%d",&x,&y,&z);directed = z;}}edge[MAXE];struct MaxFlow{int head[MAX],total;int next[MAXE],aim[MAXE],flow[MAXE];int deep[MAX];void Initialize() {total = 1;memset(head,0,sizeof(head));}void Add(int x,int y,int f) {next[++total] = head[x];aim[total] = y;flow[total] = f;head[x] = total;}void Insert(int x,int y,int f) {Add(x,y,f);Add(y,x,0);}bool BFS() {static queue<int> q;while(!q.empty())q.pop();memset(deep,0,sizeof(deep));deep[S] = 1;q.push(S);while(!q.empty()) {int x = q.front(); q.pop();for(int i = head[x]; i; i = next[i])if(flow[i] && !deep[aim[i]]) {deep[aim[i]] = deep[x] + 1;q.push(aim[i]);if(aim[i] == T)return true;}}return false;}int Dinic(int x,int f) {if(x == T)return f;int temp = f;for(int i = head[x]; i; i = next[i])if(deep[aim[i]] == deep[x] + 1 && flow[i] && temp) {int away = Dinic(aim[i],min(flow[i],temp));flow[i] -= away;flow[i^1] += away;temp -= away;}return f - temp;}}solver;int _T;int points,edges;int in[MAX],out[MAX];int sum;inline bool Euler(){sum = 0;for(int i = 1; i <= points; ++i) {int degree = out[i] - in[i];if(degree&1)return false;degree >>= 1;if(degree > 0)solver.Insert(S,i,degree),sum += degree;elsesolver.Insert(i,T,-degree);}return true;}int main(){for(cin >> _T; _T--;) {solver.Initialize();memset(in,0,sizeof(in));memset(out,0,sizeof(out));scanf("%d%d",&points,&edges);for(int i = 1; i <= edges; ++i) {edge[i].Read();if(edge[i].x == edge[i].y)continue;if(!edge[i].directed)solver.Insert(edge[i].x,edge[i].y,1);++in[edge[i].y],++out[edge[i].x];}if(!Euler()) {puts("impossible");continue;}int max_flow = 0;while(solver.BFS())max_flow += solver.Dinic(S,INF);if(max_flow == sum)puts("possible");elseputs("impossible");}return 0;}