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

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题目链接：http://acm.acmcoder.com/showproblem.php?pid=2444

题意：判断所有人是否分为两个集合，每个集合里的人互不相识。

思路：先判断是否为二分图，是的话求最大匹配，否则输出“No”。

代码：

#include <stdio.h>#include <ctime>#include <math.h>#include <limits.h>#include <complex>#include <string>#include <functional>#include <iterator>#include <algorithm>#include <vector>#include <stack>#include <queue>#include <set>#include <map>#include <list>#include <bitset>#include <sstream>#include <iomanip>#include <fstream>#include <iostream>#include <ctime>#include <cmath>#include <cstring>#include <cstdio>#include <time.h>#include <ctype.h>#include <string.h>#include <assert.h>using namespace std;int n, k;int a, b;const int MAXN = 5010;//点const int MAXM = 50010;//边struct  Edge{    int to;    int next;}edge[MAXM];int head[MAXN], tot;void init(){    tot = 0;    memset(head,-1,sizeof(head));}void addedge(int u,int v){    edge[tot].to = v;    edge[tot].next = head[u];    head[u] = tot++;}int linker[MAXN];bool used[MAXN];bool dfs(int u){    for (int i = head[u]; i != -1; i = edge[i].next)    {        int v = edge[i].to;        if (!used[v])        {            used[v] = true;            if (linker[v] == -1 || dfs(linker[v]))            {                linker[v] = u;                return true;            }        }    }    return false;}int hungary(){    int ans = 0;    memset(linker,-1,sizeof(linker));    for (int u = 1; u <= n; u++)    {        memset(used,false,sizeof(used));        if (dfs(u)) ans++;    }    return ans;}int color[510];bool bfs(int u)//染色法 判断二分图{    bool vis[510];    memset(vis,false,sizeof(vis));    for(int i=head[u];i != -1;i=edge[i].next)    {        int v = edge[i].to;        if (color[v] == -1)        {            color[v] = !color[u];            if (!bfs(v)) return false;        }        else if (color[v] == color[u])                return false;    }    return true;}int main(){    while (scanf("%d%d",&n,&k)!=EOF)    {        init();        while(k--)        {            scanf("%d%d",&a,&b);            addedge(a,b);            addedge(b,a);        }        memset(color,-1,sizeof(color));       //染色法 判断二分图        color[1] = 1;        if (!bfs(1))        {            puts("No");            continue;        }        int ans = hungary();        printf("%d\n",ans/2);    }    return 0;}

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