题目

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
const int maxn = 2e5 + 5, maxm = 2e3 + 5;
int a[maxn];
int nxt;//下一个应该遍历的结点
int res = 0;
int n, m;
vector<int> G[maxn];
void dfs(int u){if(u == nxt) nxt++;for(int i = 0; i < G[u].size();){//这里不写i++int v = G[u][i];if(v < nxt){//之前遍历过的结点，跳过i++;continue;} if(v > nxt){res++;dfs(nxt);//这里不i++, 等把nxt~v-1的结点遍历完再dfs(v)/*14 11 3*/}else{dfs(v);i++;}}
}
void solve(){cin >> n >> m;for(int i = 1; i <= n; i++){G[i].clear();}res = 0;for(int i = 1; i <= m; i++){int u, v;cin >> u >> v;
//         if(u == v) continue;
//         if(u > v) swap(u, v);G[u].push_back(v);G[v].push_back(u);}for(int i = 1; i <= n; i++){sort(G[i].begin(), G[i].end());//按顺序来}nxt = 1;while(nxt <= n){res++;//向nxt连一条边dfs(nxt);}cout << res - 1 << '\n';//减去向1连的一条边
}
signed main(){ios::sync_with_stdio(0);cin.tie(0);int T;cin >> T;while(T--){solve();}
}