poj1637

欧拉回路判断方法

膜板题

#include <cmath>#include <cstdio>#include <cstring>#include <iostream>using namespace std;int n,m,u,v;int in[210],out[210];int dis[210],gap[210];int sum_src,sum_sik;struct edge {int v,f,next;}e[3010];int cnt,head[210];int read_int () {char c = getchar();int re = 0;for(;c > '9' || c < '0';c = getchar());for(;c >= '0' && c <= '9';c = getchar())re = re * 10 + c - '0';return re;}void adde (int u,int v,int f) {e[cnt].v = v;e[cnt].f = f;e[cnt].next = head[u];head[u] = cnt++;e[cnt].v = u;e[cnt].f = 0;e[cnt].next = head[v];head[v] = cnt++;}int dfs (int u,int minf) {    if(u == n + 1)return minf;    int chan = n + 1,leftf = minf;        for(int i = head[u];i != -1;i = e[i].next) {          int v = e[i].v;                if(e[i].f > 0) {            if(dis[v] + 1 == dis[u]) {            int t = dfs(v,min(leftf,e[i].f));                e[i].f -= t;                  e[i ^ 1].f += t;                  leftf -= t;                                  if(dis[0] >= n + 2)return minf - leftf;                if(leftf == 0)break;            }            chan = min(chan,dis[v]);        }    }        if(leftf == minf) {        if(--gap[dis[u]] == 0)dis[0] = n + 2;        ++gap[dis[u] = chan + 1];    }        return minf - leftf;}bool sap () {int re = 0;gap[0] = n + 2;while(dis[0] < n + 2)re += dfs(0,0x3f3f3f3f);if(re == sum_src && re == sum_sik)return 1;return 0;}int main () {int T = read_int();while(T--) {memset(head,-1,sizeof head);memset(in,0,sizeof in);memset(out,0,sizeof out);memset(dis,0,sizeof dis);memset(gap,0,sizeof gap);sum_src = sum_sik = cnt = 0;n = read_int();m = read_int();for(int i = 1;i <= m;++i) {u = read_int();v = read_int();if(!read_int())adde(u,v,1);++in[v];++out[u];}bool f = 0;for(int i = 1;i <= n;++i) {if((int)abs(out[i] - in[i]) & 1 || (in[i] == 0 && out[i] == 0)) {f = 1;break;}if(out[i] - in[i] > 0) {adde(0,i,(out[i] - in[i]) >> 1);sum_src += (out[i] - in[i]) >> 1;}if(out[i] - in[i] < 0) {adde(i,n + 1,(in[i] - out[i]) >> 1);sum_sik += (in[i] - out[i]) >> 1;}}if(f) {printf("impossible\n");continue;}if(sap())printf("possible\n");else printf("impossible\n");}}