POJ 2239 Selecting Courses（最大匹配数）

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题目地址：http://poj.org/problem?id=2239

思路：建图的过程挺巧妙的通过(p-1)*12+q，把时间点固定在一个点上，二分图的左边是课程，右边是时间，跑一遍匈牙利算法即可，注意课程的编号不能从0开始，否则会造成给某个时间已经给0号课程用了，程序会认为没用，因为hus的数组，初始值就是0 ，你要实在想从0开始，记得把hus数组初始值赋为-1，程序里面还要再改，会比较麻烦

AC代码：

#include <iostream>#include <cstdio>#include <cstdlib>#include <algorithm>#include <queue>#include <stack>#include <map>#include <cstring>#include <climits>#include <cmath>#include <cctype>const int inf = 0x3f3f3f3f;//1061109567typedef long long LL;#define lson l,m,rt<<1#define rson m+1,r,rt<<1|1using namespace std;int map1[310][100],hus[310],visit[310];int n;bool find1(int x){    for(int i=1; i<=100; i++)    {        if(map1[x][i] && !visit[i])        {            visit[i] = 1;            if(!hus[i] || find1(hus[i]))            {                hus[i] = x;                return true;            }        }    }    return false;}int main(){    while(scanf("%d",&n) != EOF)    {        memset(map1,0,sizeof(map1));        memset(hus,0,sizeof(hus));        for(int i=1; i<=n; i++)        {            int t,p,q;            scanf("%d",&t);            for(int j=0; j<t; j++)            {                scanf("%d%d",&p,&q);                int sum = (p - 1) * 12 + q;                map1[i][sum] = 1;            }        }        int sum1 = 0;        for(int i=1; i<=n; i++)        {            memset(visit,0,sizeof(visit));            if(find1(i))                sum1++;        }        printf("%d\n",sum1);    }    return 0;}

错误代码：

#include <iostream>#include <cstdio>#include <cstdlib>#include <algorithm>#include <queue>#include <stack>#include <map>#include <cstring>#include <climits>#include <cmath>#include <cctype>const int inf = 0x3f3f3f3f;//1061109567typedef long long LL;#define lson l,m,rt<<1#define rson m+1,r,rt<<1|1using namespace std;int map1[310][100],hus[310],visit[310];int n;bool find1(int x){    for(int i=0; i<100; i++)    {        if(map1[x][i] && !visit[i])        {            visit[i] = 1;            if(!hus[i] || find1(hus[i]))            {                hus[i] = x;                return true;            }        }    }    return false;}int main(){    while(scanf("%d",&n) != EOF)    {        memset(map1,0,sizeof(map1));        memset(hus,0,sizeof(hus));        for(int i=0; i<n; i++)        {            int t,p,q;            scanf("%d",&t);            for(int j=0; j<t; j++)            {                scanf("%d%d",&p,&q);                int sum = (p - 1) * 12 + q;                map1[i][sum] = 1;            }        }        int sum1 = 0;        for(int i=0; i<n; i++)        {            memset(visit,0,sizeof(visit));            if(find1(i))//不能从0开始找，因为有可能某节课被0占用了，却被认为这节课没被占用，因为数组hus的初值就是0                sum1++;        }        printf("%d\n",sum1);    }    return 0;}

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