POJ1236 Network of Schools

来源：互联网发布：淘宝卖家账号是什么编辑：程序博客网时间：2024/06/10 02:47

PS: 强连通，缩点。注意不要忘记考虑图是强连通的情况，WA了4次。省赛热身。

#include <iostream>#include <cstdio>#include <algorithm>#include <cstring>#include <vector>#include <stack>using namespace std;const int maxn = 110;vector<int> G[maxn];vector<int> G1[maxn];vector<int> RG1[maxn];int n;int low[maxn], pre[maxn], sccno[maxn];int dfs_clock, scc_cnt;stack<int> S;void dfs(int u) {    low[u] = pre[u] = ++dfs_clock;    S.push(u);    for(int i = 0; i < (int)G[u].size(); i++) {        int v = G[u][i];        if(!pre[v]) {            dfs(v);            low[u] = min(low[u], low[v]);        } else if(!sccno[v]) {            low[u] = min(low[u], low[v]);        }    }    if(pre[u]==low[u]) {        scc_cnt++;        for(;;) {            int x = S.top(); S.pop();            sccno[x] = scc_cnt;            if(x==u) break;        }    }}void find_scc() {    while(!S.empty()) S.pop();    memset(sccno, 0, sizeof(sccno));    memset(pre, 0, sizeof(pre));    memset(low, 0, sizeof(low));    scc_cnt = 0; dfs_clock = 0;    for(int i = 1; i <= n; i++) {        if(!pre[i]) dfs(i);    }}void build_DAG() {    int s, t;    for(int i = 1; i <= scc_cnt; i++) {        G1[i].clear();        RG1[i].clear();    }    for(int i = 1; i <= n; i++) {        for(int j = 0; j < (int)G[i].size(); j++) {            int v = G[i][j];            s = sccno[i]; t = sccno[v];            if(s!=t) {                G1[s].push_back(t);                RG1[t].push_back(s);            }        }    }}void work() {    int ans1 = 0, ans2 = 0;    for(int i = 1; i <= scc_cnt; i++) {        if(!RG1[i].size()) {            ans1++;        }    }    for(int i = 1; i <= scc_cnt; i++) {        if(!G1[i].size()) {            ans2++;        }    }    if(scc_cnt==1) {  // WA.        printf("1\n0\n");        return;    }    printf("%d\n", ans1);    printf("%d\n", max(ans1, ans2));}int main(){    int x;    while(scanf("%d", &n)!=EOF) {        for(int i = 1; i <= n; i++) G[i].clear();        for(int i = 1; i <= n; i++) {            for(;;)  {                scanf("%d", &x);                if(x!=0) G[i].push_back(x);                else break;            }        }        find_scc();        build_DAG();        work();    }    return 0;}

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