POJ 1637 最大流+欧拉回路

#include<cstring>
#include<iostream>
#include<iomanip>
#include<queue>
#include<cmath>
#include<stack>
#include<map>
#include<vector>
#include<set>
#include<algorithm>
using namespace std;
typedef long long LL;
const int int_max = 0x07777777;
const int int_min = 0x80000000;
const int maxn = 250;

struct Edge{
    int from, to, cap, flow;
    Edge(int _from, int _to, int _cap, int _flow):from(_from),to(_to),cap(_cap),flow(_flow){}
};
vector<Edge> es;
vector<int> g[maxn];
int s,t;
int p[maxn],d[maxn],gap[maxn],cur[maxn];
void addedge (int from, int to, int cap){
    es.push_back(Edge(from, to, cap, 0));
    es.push_back(Edge(to, from, 0,0));
    int num = es.size();
    g[from].push_back(num-2);
    g[to].push_back(num-1);
}
void BFS (){
    queue<int> q;
    memset(d, -1, sizeof(d));
    d[t] = 0;
    q.push(t);
    while(!q.empty()){
        int u = q.front();
        q.pop();
        for(int i = 0; i < g[u].size(); i++){
            Edge& e = es[g[u][i]];
            if(g[u][i]&1 && d[e.to]==-1){
                d[e.to] = d[u]+1;
                q.push(e.to);
            }
        }
    }
}
int augment (){
    int x = t;
    int a = int_max;
    while(x!=s){
        Edge& e = es[p[x]];
        a = (a < e.cap-e.flow ? a : e.cap-e.flow);
        x = es[p[x]].from;
    }
    x = t;
    while(x!=s){
        es[p[x]].flow += a;
        es[p[x]^1].flow -= a;
        x = es[p[x]].from;
    }
    return a;
}
int sap (){
    int flow = 0;
    BFS();
    memset(gap, 0, sizeof(gap));
    for(int i = 0; i <= t; i++) if(d[i]!=-1) gap[d[i]]++;
    int x = s;
    memset(cur, 0, sizeof(cur));
    while(d[s] < t+1){
        if(x==t){
            flow += augment();
            x = s;
        }
        int ok = 0;
        for(int i = 0; i < g[x].size(); i++){
            Edge& e = es[g[x][i]];
            if(e.cap > e.flow && d[x]==d[e.to]+1){
                ok = 1;
                p[e.to] = g[x][i];
                cur[x] = i;
                x = e.to;
                break;
            }
        }
        if(!ok){
            int mm = t;
            for(int i = 0; i < g[x].size(); i++){
                Edge& e = es[g[x][i]];
                if(e.cap > e.flow) mm = (mm > d[e.to] ? d[e.to] : mm);
            }
            if(--gap[d[x]] == 0) break;
            gap[d[x]=mm+1]++;
            cur[x] = 0;
            if(x!=s) x = es[p[x]].from;
        }
    }
    return flow;
}
int n,m;
int main(int argc, const char * argv[])
{
    int T;
    scanf("%d", &T);
    while(T--){
        scanf("%d %d", &n, &m);
        es.clear();
        for(int i = 0; i < maxn; i++) g[i].clear();
        s = 0;
        t = n+1;
        int ru[maxn],chu[maxn],rr[maxn];
        memset(ru, 0, sizeof(ru));
        memset(chu, 0, sizeof(chu));
        memset(rr, 0, sizeof(rr));
        for(int i = 0; i < m; i++){
            int x,y,z;
            scanf("%d %d %d", &x, &y, &z);
            if(x==y) continue;
            if(z==0){
                addedge(x, y, 1);
                addedge(y, x, 1);
                rr[x]++;
                rr[y]++;
            }else{
                chu[x]++;
                ru[y]++;
            }
        }
        int total = 0;
        for(int i = 1; i <= n; i++){
            if(ru[i]-chu[i] > 0) addedge(s, i, ru[i]-chu[i]);
            if(chu[i]-ru[i] > 0) addedge(i, t, chu[i]-ru[i]);
            if(ru[i] > chu[i]) total += ru[i]-chu[i];
        }
        if(total==0){
            int flag = 1;
            for(int i = 1; i <= n; i++){
                if(rr[i]&1){
                    flag = 0;
                    break;
                }
            }
            if(flag) cout << "possible" << endl;
            else cout << "impossible" << endl;
            continue;
        }
        int result = sap();
        if(result==total) cout << "possible" << endl;
        else cout << "impossible" << endl;
    }
}