hdu 2444 The Accomodation of Students 二分图判断 + 最大匹配

题目链接

题意：给定n个点，m条无向边。首先判断能否得到一个二分图（BFS），如果可以，则进行二分图匹配。

#include <stdio.h>#include <string.h>#include <math.h>#include <iostream>#include <algorithm>using namespace std;typedef long long LL;const int maxn = 205;const int Mod = 1000000007;int n,m;bool vis[maxn];int cx[maxn],cy[maxn];int map[maxn][maxn],c[maxn];bool bipartite( int u ){for( int i = 1; i <= n; i ++ ){if( map[u][i] ){if( c[u] == c[i] )return false;if( !c[i] ){c[i] = 3 - c[u];if( !bipartite(i) )  return false;  }}}return true;}int findpath( int u ){for( int i = 1; i <= n; i ++ ){if( c[i] == 2 && map[u][i] && !vis[i] ){vis[i] = 1;if( cy[i] == -1 || findpath( cy[i] ) ){cy[i] = u;cx[u] = i;return true;}}}return false;}int MaxMatch(){int ans = 0;memset( cx,-1,sizeof(cx) );memset( cy,-1,sizeof(cy) );for( int i = 1; i <= n; i ++ ){if( c[i] == 1 && cx[i] == -1 ){memset( vis,0,sizeof(vis) );ans += findpath( i );}}return ans;}int main(){int a,b;while( scanf("%d%d",&n,&m) != EOF ){memset( c,0,sizeof(c) );memset( map,0,sizeof(map) );for( int i = 0; i < m; i ++ ){scanf("%d%d",&a,&b);map[a][b] = map[b][a] = 1;}int ok = 1;for( int i = 1; i <= n; i ++ ){if( c[i] == 0 )c[i] = 1;if( !bipartite( i ) )ok = 0;}if( ok ){printf("%d\n",MaxMatch());}elseputs("No");}return 0;}