CodeForces 687A - NP-Hard Problem(二分图染色)
题意:给定n个顶点和m条边的无向图,求能否构成二分图,若能,输出两个顶点集,否则输出 -1
对某个顶点,对于有边与它相连的其他点,染成与它不同的颜色,然后再研究这些点,继续染与它们有关系的点,直到所有有边相连的点都被染色完毕。
不能构成:若要染的顶点之前已经被染成同样的颜色,则不能构成二分图。
孤立顶点不作研究。
#include<cstdio> #include<cstring> #include<cctype> #include<cstdlib> #include<cmath> #include<iostream> #include<sstream> #include<iterator> #include<algorithm> #include<string> #include<vector> #include<set> #include<map> #include<deque> #include<queue> #include<stack> #include<list> typedef long long ll; typedef unsigned long long llu; const int MAXN = 100 + 10; const int MAXT = 100000 + 10; const int INF = 0x7f7f7f7f; const double pi = acos(-1.0); const double EPS = 1e-6; using namespace std; int n, m, vis[MAXT]; vector<int> e[MAXT]; bool dfs(int lur, int t){ int len = e[lur].size(); if(!len) return true; vis[lur] = t; for(int i = 0; i < len; ++i){ int &tmp = e[lur][i]; if(vis[tmp] == -t) continue; else if(vis[tmp] == t) return false; if(!dfs(tmp, -t)) return false; } return true; } int main(){ memset(vis, 0, sizeof vis); scanf("%d%d", &n, &m); int a, b; for(int i = 0; i < m; ++i){ scanf("%d%d", &a, &b); e[a].push_back(b); e[b].push_back(a); } bool flag = true; for(int i = 1; i <= n; ++i){ if(vis[i]) continue; if(!e[i].size()){ vis[i] = 2; continue; } if(!dfs(i, 1)){ flag = false; break; } } if(!flag) printf("-1\n"); else{ e[0].clear(); e[1].clear(); for(int i = 1; i <= n; ++i) if(vis[i] == 1) e[0].push_back(i); else if(vis[i] == -1) e[1].push_back(i); a = e[0].size(); printf("%d\n", a); for(int i = 0; i < a; ++i){ if(i) printf(" "); printf("%d", e[0][i]); } a = e[1].size(); printf("\n%d\n", a); for(int i = 0; i < a; ++i){ if(i) printf(" "); printf("%d", e[1][i]); } printf("\n"); } return 0; }