【二分图匹配入门专题1】E

Consider a town where all the streets are one-way and each street leads from one intersection to another. It is also known that starting from an intersection and walking through town's streets you can never reach the same intersection i.e. the town's streets form no cycles. 

With these assumptions your task is to write a program that finds the minimum number of paratroopers that can descend on the town and visit all the intersections of this town in such a way that more than one paratrooper visits no intersection. Each paratrooper lands at an intersection and can visit other intersections following the town streets. There are no restrictions about the starting intersection for each paratrooper. 

InputYour program should read sets of data. The first line of the input file contains the number of the data sets. Each data set specifies the structure of a town and has the format: 

no_of_intersections 
no_of_streets 
S1 E1 
S2 E2 
...... 
Sno_of_streets Eno_of_streets 

The first line of each data set contains a positive integer no_of_intersections (greater than 0 and less or equal to 120), which is the number of intersections in the town. The second line contains a positive integer no_of_streets, which is the number of streets in the town. The next no_of_streets lines, one for each street in the town, are randomly ordered and represent the town's streets. The line corresponding to street k (k <= no_of_streets) consists of two positive integers, separated by one blank: Sk (1 <= Sk <= no_of_intersections) - the number of the intersection that is the start of the street, and Ek (1 <= Ek <= no_of_intersections) - the number of the intersection that is the end of the street. Intersections are represented by integers from 1 to no_of_intersections. 

There are no blank lines between consecutive sets of data. Input data are correct. 
OutputThe result of the program is on standard output. For each input data set the program prints on a single line, starting from the beginning of the line, one integer: the minimum number of paratroopers required to visit all the intersections in the town. 
Sample Input

2
4
3
3 4
1 3
2 3
3
3
1 3
1 2
2 3

Sample Output

2
1
题意：给你n个路口，m条街道，每行输入路口a到路口b，伞兵只能沿着一条路走下去，没有环形街道，问最少需要多少伞兵才能访问所有路口。
思路：最小路径覆盖=顶点数-最大匹配数。
看到翻译的时候我是崩溃的，作为我们队的翻译，我居然沦落到看别人翻译的地步，立个flag，除非我把题目所有单词
查完还不知道题意，否则绝对不百度翻译，话说，二分图建模好痛苦啊，我对这种题目一点想法都没有，实在不行的话，以后这种题丢给队友好了

#include<stdio.h>
#include<string.h>
#define N 500
int book[N],match[N],e[N][N];
int n,m;

int dfs(int u)
{
    int i;
    for(i = 1; i <= n; i ++)
    {
        if(!book[i]&&e[u][i])
        {
            book[i] = 1;
            if(!match[i]||dfs(match[i]))
            {
                match[i] = u;
                return 1;
            }
        }
    }
    return 0;
}
int main()
{
    int i,t,j,sum,t1,t2;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        scanf("%d",&m);
        
        memset(e,0,sizeof(e));
        memset(match,0,sizeof(match));
        for(i = 1; i <= m; i ++)
        {
            scanf("%d%d",&t1,&t2);
            e[t1][t2] = 1;
        }
        sum = 0;
        for(i = 1; i <= n; i ++)
        {
            memset(book,0,sizeof(book));
            if(dfs(i))
                sum ++;
        }
        printf("%d
",n-sum);
    }
    return 0;
}