Hdu2444二分图

给你一个图，问是否为二分图，若是求出最大匹配。

并查集判图，原理黑白染色。

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <stack>
#include <queue>
#include <vector>
#include <map>
#include <string>
#include <iostream>
using namespace std;

int n,m;
const int maxn = 555;
int link[maxn];
int used[maxn];
int Map[maxn][maxn];
int father[maxn*2];
int getfather(int x)
{
    if(father[x]!=x) father[x]=getfather(father[x]);
    return father[x];
}

int dfs(int x)
{
    for(int i=1;i<=n;i++){
        if(Map[x][i]&&!used[i]){
            used[i]=1;
            if(link[i]==-1||dfs(link[i])){
                link[i]= x; return 1;
            }
        }
    }
    return 0;
}

int gao()
{
    int ans=0;
    memset(link,-1,sizeof(link));
    for(int i=1;i<=n;i++){
        memset(used,0,sizeof(used));
        ans+=dfs(i);
    }
    return ans;
}

int main()
{
    int a,b;
    while(cin>>n>>m){
        memset(Map,0,sizeof(Map));
        for(int i=1;i<=2*n;i++)
        father[i]= i;
        int flag=0;
        for(int i=0;i<m;i++){
            scanf("%d%d",&a,&b);
            int fa=getfather(a);int fb= getfather(b); int fa1= getfather(a+n);int fb1= getfather(b+n);
            if(fa==fb) flag=1;
            father[fa]=fb1;father[fb]=fa1;
            Map[a][b]=1;Map[b][a]=1;
        }
        if(flag){
            printf("No
");continue;
        }
        int t= gao();
        printf("%d
",t/2);
    }
    return 0;
}

 bfs判图

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <stack>
#include <queue>
#include <vector>
#include <map>
#include <string>
#include <iostream>
using namespace std;

int n,m;
const int maxn = 222;
int link[maxn];
int used[maxn];
int Map[maxn][maxn];
int Dye(int x)
{
    int vis[maxn];int color[maxn];
    memset(vis,0,sizeof(vis));
    memset(color,-1,sizeof(color));
    queue<int> q;
    q.push(x);
    vis[x]=1; color[x]= 1;
    while(!q.empty()){
        int cur=q.front(); q.pop();
        for(int i=1;i<=n;i++){
            if(!Map[cur][i])continue;
            if(color[i]==color[cur]) return 0;
            color[i]=color[cur]^1;
            if(!vis[i]){
                vis[i]=1 ;q.push(i);
            }
        }
    }
    return 1;
}

int dfs(int x)
{
    for(int i=1;i<=n;i++){
        if(Map[x][i]&&!used[i]){
            used[i]=1;
            if(link[i]==-1||dfs(link[i])){
                link[i]= x; return 1;
            }
        }
    }
    return 0;
}

int gao()
{
    int ans=0;
    memset(link,-1,sizeof(link));
    for(int i=1;i<=n;i++){
        memset(used,0,sizeof(used));
        ans+=dfs(i);
    }
    return ans;
}

int main()
{
    int a,b;
    while(cin>>n>>m){
        memset(Map,0,sizeof(Map));
        for(int i=0;i<m;i++){
            scanf("%d%d",&a,&b);
            Map[a][b]=1;Map[b][a]=1;
        }
        int flag=0;
        for(int i=1;i<=n;i++)
            if(!Dye(i)) flag=1;
        if(flag){
            printf("No
");continue;
        }
        int t= gao();
        printf("%d
",t/2);
    }
    return 0;
}