poj2942 点双连通分量

#include <stdio.h>

#include <string.h>

#define MAXN 1100

#define MAXM 1000100

#define MIN(a, b) ((a) < (b) ? (a) : (b))

struct EDGE{

int to, next;

}edges[MAXM];

int map[MAXN][MAXN], ans[MAXN][MAXN], dfn[MAXN], low[MAXN],total, top, n, times, res;

int strack[MAXN], colour[MAXN], can[MAXN];

void dfs(int u){

dfn[strack[top++] = u] = low[u] = ++times;

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

if(!map[u][i] && i != u)

if(dfn[i]) low[u] = MIN(low[u], dfn[i]);

else{

dfs(i);

low[u] = MIN(low[u], low[i]);

if(dfn[u] <= low[i]){

for(strack[top] = -1, ans[total][0] = u, res = 1; strack[top]!= i; ans[total][res ++] = strack[--top]);

if(res > 2)

ans[total++][res++] = -1;

}

}

}

void tarjan(){

int i;

times = top = total = 0;

memset(dfn, 0, sizeof(dfn));

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

if(!dfn[i]) dfs(i);

}

void drow(int fa, int now, int co){

if(res) return;

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

if(!map[now][i] && now != i&& i != fa&& colour[i])

if(colour[i] == 1){

colour[i] = 5 - co;

drow(now, i, 5 - co);

}

else 

if(colour[i] == colour[now]){res = 1; return;}

}

void set_colour(int t){

int k = 0;

while(ans[t][k] != -1)

colour[ans[t][k ++]] = 1;

colour[ans[t][0]] = 2;

res = 0;

drow(-1, ans[t][0], 2);

k = 0;

while(ans[t][k] != -1){

colour[ans[t][k]] = 0;

if(res) can[ans[t][k]] = 1;

++k;

}

}

int Get_ans(){

int i, ans = 0;

memset(can, 0, sizeof(can));

memset(colour, 0, sizeof(colour));

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

set_colour(i);

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

if(!can[i]) ans ++;

return ans;

}

int main(){

int m, i, x, y;int a[10], now = 5;

while(~scanf("%d %d", &n, &m),n){

memset(map, 0, sizeof(map));

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

scanf("%d %d", &x, &y);

map[x][y] = map[y][x] = 1;

}

tarjan();

printf("%d\n", Get_ans());

}

return 0;

}