codevs2171 棋盘覆盖

#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#include<vector> 
#include<queue>
#include<algorithm>
#define maxn 105
#define __maxNodes 13145
using namespace std;
// 顶点、边的编号均从 0 开始
// 邻接表储存

vector<int> G[__maxNodes]; /* G[i] 存储顶点 i 出发的边的编号 */
typedef vector<int>::iterator iterator_t;
int num_nodes;
int num_left;
int num_right;
int num_edges;
int matching[__maxNodes]; /* 存储求解结果 */
int check[__maxNodes];
int n,m,rec[maxn][maxn],cnt;
int dx[4] = {-1,0,1,0};
int dy[4] = {0,-1,0,1};
bool judge(int y,int x){
    if(x < 1 || x > n || y < 1 || y > n || rec[y][x]) return false;
    else return true;
}
bool dfs(int u)
{
    for (iterator_t i = G[u].begin(); i != G[u].end(); ++i) { // 对 u 的每个邻接点
        int v = *i;
        if (!check[v]) {     // 要求不在交替路中
            check[v] = true; // 放入交替路
            if (matching[v] == -1 || dfs(matching[v])) {
                // 如果是未盖点，说明交替路为增广路，则交换路径，并返回成功
                matching[v] = u;
                matching[u] = v;
                return true;
            }
        }
    }
    return false; // 不存在增广路，返回失败
}

int hungarian()
{
    int ans = 0;
    memset(matching, -1, sizeof(matching));
    for (int u=0; u < num_left; ++u) {
        if (matching[u] == -1) {
            memset(check, 0, sizeof(check));
            if (dfs(u))
                ++ans;
        }
    }
    return ans;
}
int main(){
    cin>>n>>m;
    int x,y;
    for(int i = 1;i <= m;i++){
        scanf("%d%d",&y,&x);
        rec[y][x] = 1;
    }
    int cu,cv;
    for(int i = 1;i <= n;i++){
        for(int j = 1;j <= n;j++){
            if(rec[i][j]) continue;
            for(int k = 0;k < 4;k++){
                int ny = i + dy[k];
                int nx = j + dx[k];
                if(judge(ny,nx)){
                    cu = (i-1)*n+j-1;
                    cv = (ny-1)*n+nx-1;
                    G[cu].push_back(cv);
                    
                }
            }
        }
    }
    num_left = n*n;
    cout<<hungarian();
    return 0;
}