https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=2021

題解：二分圖判斷

/* *@Author: STZG *@Language: C++ */ #include <bits/stdc++.h> #include<iostream> #include<algorithm> #include<cstdlib> #include<cstring> #include<cstdio> #include<string> #include<vector> #include<bitset> #include<queue> #include<deque> #include<stack> #include<cmath> #include<list> #include<map> #include<set> //#define DEBUG #define RI register int #define endl "\n" using namespace std; typedef long long ll; //typedef __int128 lll; const int N=100000+10; const int M=100000+10; const int MOD=1e9+7; const double PI = acos(-1.0); const double EXP = 1E-8; const int INF = 0x3f3f3f3f; int t,n,m,k,p,l,r,u,v; int ans,cnt[2],flag,temp,sum; int col[N]; char str; struct node{}; vector<int>G[N]; bool dfs(int u,int color){col[u]=color;cnt[color]++;for(int i=0,j=G[u].size();i<j;i++){int v=G[u][i];if(col[u]==col[v])return 0;if(col[v]==-1&&!dfs(v,!color))return 0;}return 1; } void init(){for(int i=0;i<n;i++){G[i].clear();}memset(col,-1,sizeof(col));ans=1;sum=0; } int main() { #ifdef DEBUGfreopen("input.in", "r", stdin);//freopen("output.out", "w", stdout); #endif//ios::sync_with_stdio(false);//cin.tie(0);//cout.tie(0);scanf("%d",&t);while(t--){scanf("%d%d",&n,&m);init();for(int i=1;i<=m;i++){scanf("%d%d",&u,&v);G[u].push_back(v);G[v].push_back(u);}for(int i=0;i<n;i++){if(col[i]==-1){memset(cnt,0,sizeof(cnt));ans&=dfs(i,1);if(ans){if(cnt[0]+cnt[1]==1){sum++;}else{sum+=min(cnt[0],cnt[1]);}}}}if(ans){cout<<sum<<endl;}else{cout<<-1<<endl;}}#ifdef DEBUGprintf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC); #endif//cout << "Hello world!" << endl;return 0; }

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