[USACO5.3]校园网Network of Schools

P2746 [USACO5.3]校园网Network of Schools

缩点

蒟蒻在这道题上wa了六次……

错误一：

结论推错了

任务B的答案是根数和叶子数中较小的那个

也就是说加路前的各个树加路之后不一定是强连通分量

错误二：

特判 当只有一个点的时候 任务二输出0

int main(){
    init();
    for(int i = 1; i <= n; i++)
       if(!dfn[i]) tarjan(i);
    for(int i = 1; i <= esize[0]; i++){
        int vv = edge[0][i].v, uu = edge[0][i].u;
        if(col[uu] != col[vv]){
            addedge(col[uu], col[vv], 1);
            ind[col[vv]]++;
            out[col[uu]]++;
        }
    }
    int ans1 = 0, ans2 = 0;
    for(int i = 1; i <= csize; i++){
        if(!ind[i]) ans1++;
        if(!out[i]) ans2++;
    }
    printf("%d
", ans1);
    if(csize == 1) printf("0
");
    else printf("%d
", max(ans1, ans2));
    return 0;
}

void tarjan(int x){
//    printf("%d
", x);
    low[x] = dfn[x] = ++dc;
    s.push(x); ins[x] = 1;
    for(int i = head[0][x]; i != -1; i = edge[0][i].next){
        int vv = edge[0][i].v;
        if(!dfn[vv]){
            tarjan(vv);
            low[x] = min(low[x], low[vv]);
        }
        else if(ins[vv]) low[x] = min(low[x], low[vv]);
    }
    if(dfn[x] == low[x]){
        ++csize;
        int top;
        do{
            top = s.top(); s.pop();
            col[top] = csize;
            ins[top] = 0;
        }
        while(top != x);
    }
}