# Poj Solution 1637

```http://poj.org/problem?id=1637

//* @author
import java.util.*;
import java.util.concurrent.ArrayBlockingQueue;

public class Main {
static int N = 205;
static int [] degin, degout, deg, pre;
static int [][] cap;

private static int maxflow(int s, int t, int size) {
Queue<Integer> que = new ArrayBlockingQueue<Integer>(N);
int flow = 0, i, ext;

while(true) {
for(i = 0;i < size;++ i)
pre[i] = -1;
pre[s] = s;
que.clear();
while(!que.isEmpty()) {
int k = que.poll();
for(i = 0;i < size;++ i) {
if(pre[i] == -1 && cap[k][i] > 0) {
pre[i] = k;
if(i == t) break;
}
}
}

if(pre[t] == -1) break;

ext = cap[pre[t]][t];
for(i = t;i != s;i = pre[i]) {
if(ext > cap[pre[i]][i])
ext = cap[pre[i]][i];
}
flow += ext;
for(i = t;i != s;i = pre[i]) {
cap[pre[i]][i] -= ext;
cap[i][pre[i]] += ext;
}
}
return flow;
}

public static void main(String [] args) {
Scanner cin = new Scanner(System.in);
int n, m, s, a, b, d, i, j, p;
degin = new int [N];
degout = new int [N];
deg = new int [N];
pre = new int [N];
cap = new int [N][N];

n = cin.nextInt();
while(n -- > 0) {
m = cin.nextInt();
s = cin.nextInt();
for(i = 0;i < m + 2;++ i) {
degin[i] = degout[i] = deg[i] = 0;
for(j = 0;j < m + 2;++ j)
cap[i][j] = 0;
}
p = 0;

for(i = 0;i < s;++ i) {
a = cin.nextInt();
b = cin.nextInt();
d = cin.nextInt();
if(d == 0) {
deg[a]++;
deg[b]++;
cap[0][a]++;
cap[a][b]++;
++p;
}
else {
degout[a]++;
degin[b]++;
}
}

Boolean flag = true;
for(i = 1;i <= m;++ i) {
int k = degin[i] + degout[i] + deg[i];
if(k % 2 == 1 || k / 2 < degin[i] || k / 2 < degout[i]) {
flag = false;
break;
}
cap[i][m + 1] = k / 2 - degin[i];
}

if(flag && maxflow(0, m + 1, m + 2) == p)
System.out.println("possible");
else
System.out.println("impossible");
}
}
}

```
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