uva 1364

刘书上例题

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <set>
#include <stack>
#include <vector>
#include <sstream>
#include <cstring>
#include <string>
#include <map>
#include <queue>
#include <algorithm>
#include <iostream>
#define FFI freopen("in.txt", "r", stdin)
#define maxn 1010
#define INF 0x3f3f3f3f
#define inf 10000000
#define MOD 1000000007
#define ULL unsigned long long
#define LL long long
#define _setm(houge) memset(houge, INF, sizeof(houge))
#define _setf(houge) memset(houge, -1, sizeof(houge))
#define _clear(houge) memset(houge, 0, sizeof(houge))
using namespace std;

struct Edge
{
    int u, v;
};

int color[maxn], pre[maxn], iscut[maxn], bccno[maxn], dfs_clock, bcc_cnt;
vector<int> G[maxn], bcc[maxn];
stack<Edge> S;
int A[maxn][maxn], odd[maxn];

bool bipartite(int u, int b) {
    for(int i = 0; i < (int)G[u].size(); ++ i) {
        int v = G[u][i];
        if(bccno[v] != b) continue;
        if(color[v] == color[u]) return false;
        if(!color[v]) {
            color[v] = 3-color[u];
            if(!bipartite(v, b)) return false;
        }
    }
    return true;
}

int dfs(int u, int fa) {
    int lowu = pre[u] = ++ dfs_clock;
    int child = 0;
    for(int i = 0; i < (int)G[u].size(); ++ i) {
        int v = G[u][i];
        Edge e = (Edge){u, v};
        if(!pre[v]) {
            S.push(e);
            child ++;
            int lowv = dfs(v, u);
            lowu = min(lowu, lowv);
            if(lowv >= pre[u]) {
                iscut[u] = true;
                bcc_cnt ++;
                bcc[bcc_cnt].clear();
                for(;;) {
                    Edge x = S.top();
                    S.pop();
                    if(bccno[x.u] != bcc_cnt) {
                        bcc[bcc_cnt].push_back(x.u);
                        bccno[x.u] = bcc_cnt;
                    }
                    if(bccno[x.v] != bcc_cnt) {
                        bcc[bcc_cnt].push_back(x.v);
                        bccno[x.v] = bcc_cnt;
                    }
                    if(x.u == u && x.v == v) break;
                }
            }
        }
        else if(pre[v] < pre[u] && v != fa) {
            S.push(e);
            lowu = min(lowu, pre[v]);
        }
    }
    if(fa < 0 && child == 1) iscut[u] = 0;
    return lowu;
}

void find_bcc(int n) {
    _clear(pre);
    _clear(iscut);
    _clear(bccno);
    dfs_clock = bcc_cnt = 0;
    for(int i = 0; i < n; ++ i) {
        if(!pre[i]) dfs(i, -1);
    }
}

int main() {
    int n, m;
    // FFI;
    while(scanf("%d%d", &n, &m) == 2 && n) {
        for(int i = 0; i < n; ++ i) G[i].clear();
        _clear(A);
        for(int i = 0; i < m; ++ i) {
            int u, v;
            scanf("%d%d", &u, &v);
            u--, v--;
            A[u][v] = A[v][u] = 1;
        }
        for(int u = 0; u < n; ++ u) {
            for(int v = u+1; v < n; ++ v) {
                if(!A[u][v]) {
                    G[u].push_back(v);
                    G[v].push_back(u);
                }
            }
        }
        find_bcc(n);
        _clear(odd);
        for(int i = 1; i <= bcc_cnt; ++ i) {
            _clear(color);
            for(int j = 0; j < (int)bcc[i].size(); ++ j) {
                bccno[bcc[i][j]] = i;
            }
            int u = bcc[i][0];
            color[u] = 1;
            if(!bipartite(u, i)) {
                for(int j = 0; j < (int)bcc[i].size(); ++ j) {
                    odd[bcc[i][j]] = 1;
                }
            }
        }
        int ans = n;
        for(int i = 0; i < n; ++ i) if(odd[i]) --ans;
        printf("%d\n", ans);
    }
    return 0;
}