題面

Vjudge

Sol

給出一個n個點的無向圖，詢問是否為弦圖

做法見上上上篇博客

# include <bits/stdc++.h>
# define RG register
# define IL inline
# define Fill(a, b) memset(a, b, sizeof(a))
using namespace std;
const int _(1005);
typedef long long ll;

IL int Input(){
    RG int x = 0, z = 1; RG char c = getchar();
    for(; c < '0'
 
 || c > '9'; c = getchar()) z = c == '-' ? -1 : 1;
    for(; c >= '0' && c <= '9'; c = getchar()) x = (x << 1) + (x << 3) + (c ^ 48);
    return x * z;
}

int n, m, first[_], cnt, label[_], vis[_], best, Q[_], id[_], S[_];
struct Edge{
    int
 
 to, next;
} edge[_ * _];
vector <int> P[_];

IL void Add(RG int u, RG int v){
    edge[cnt] = (Edge){v, first[u]}, first[u] = cnt++;
}

IL int Check(){
    for(RG int i = 1; i <= n; ++i) vis[i] = 0;
    for(RG int i = n; i; --i){
        RG int ret = 1; S[0] = 0;
        for(RG int e = first[Q[i]]; e != -1
 
; e = edge[e].next)
            if(id[edge[e].to] > i) vis[S[++S[0]] = edge[e].to] = 1;
        for(RG int e = first[S[1]]; e != -1; e = edge[e].next)
            if(edge[e].to != S[1] && vis[edge[e].to])
                ret += (vis[edge[e].to] == 1), ++vis[edge[e].to];
        for(RG int j = 1; j <= S[0]; ++j) vis[S[j]] = 0;
        if(S[0] && ret != S[0]) return 0;
    }
    return 1;
}

int main(RG int argc, RG char* argv[]){
    while(233){
        n = Input(), m = Input();
        if(!n && !m) break;
        cnt = best = 0;
        for(RG int i = 1; i <= n; ++i) P[i].clear(), first[i] = -1, vis[i] = label[i] = 0;
        for(RG int i = 1; i <= m; ++i){
            RG int u = Input(), v = Input();
            Add(u, v), Add(v, u);
        }
        for(RG int i = 1; i <= n; ++i) P[0].push_back(i);
        for(RG int i = n, nw; i; --i){
            for(RG int flg = 0; !flg; ){
                for(RG int j = P[best].size() - 1; ~j; --j)
                    if(vis[P[best][j]]) P[best].pop_back();
                    else{
                        nw = P[best][j], flg = 1;
                        break;
                    }
                if(!flg) --best;
            }
            vis[nw] = 1, Q[i] = nw, id[nw] = i;
            for(RG int e = first[nw]; e != -1; e = edge[e].next)
                if(!vis[edge[e].to]){
                    P[++label[edge[e].to]].push_back(edge[e].to);
                    best = max(best, label[edge[e].to]);
                }
        }
        Check() ? puts("Perfect") : puts("Imperfect");
        puts("");
    }
    return 0;
}

[ZOJ1015]：Fishing Net