POJ_1422 Air Raid(二分图最大匹配匈牙利算法)

这道题其实就是二分图的最大匹配问题。用构造匈牙利树的方法可以有效的提高求解的效率。

#include <iostream>
#include <string.h>
#define MAX 121
using namespace std;

bool map[MAX][MAX];
int xM[MAX],yM[MAX];
bool cheak[MAX];
int n;

bool DFS(int u)
{
    int v = 0;
    for(v = 0;v <= n;v++)
    {
        if(!cheak[v] && map[u][v])
        {
            cheak[v] = true;
            if(yM[v] == -1 || DFS(yM[v]))
            {
                yM[v] = u;
                xM[u] = v;
                return true;
            }
        }
    }
    return false;
}

int search()
{
    int cot = 0;
    memset(xM,-1,sizeof(xM));
    memset(yM,-1,sizeof(yM));
    for(int i = 1;i <= n;i++)
    {
        if(xM[i] == -1)
        {
            memset(cheak,false,sizeof(cheak));
            if(DFS(i))
            {
                cot++;
            }
        }
    }
    return cot;
}
int main()
{
    int testnum;
    int streat;
    cin>>testnum;
    for(int i = 0;i < testnum;i++)
    {
        cin>>n>>streat;
        memset(map,false,sizeof(map));
        for(int j = 0;j < streat;j++)
        {
            int sK,eK;
            cin>>sK>>eK;
            map[sK][eK] = true;
        }
        cout<<n - search()<<endl;
    }
    return 0;
}