Chessboard POJ - 2446（最大流 || 匹配）

there is a pair of integers (x, y) in each line, which represents a hole in the y-th row, the x-th column.

呃呃呃呃呃。。。因为这个wa了一次

向周围建边就好了

#include <iostream>
#include <cstdio>
#include <sstream>
#include <cstring>
#include <map>
#include <cctype>
#include <set>
#include <vector>
#include <stack>
#include <queue>
#include <algorithm>
#include <cmath>
#include <bitset>
#define rap(i, a, n) for(int i=a; i<=n; i++)
#define rep(i, a, n) for(int i=a; i<n; i++)
#define lap(i, a, n) for(int i=n; i>=a; i--)
#define lep(i, a, n) for(int i=n; i>a; i--)
#define rd(a) scanf("%d", &a)
#define rlld(a) scanf("%lld", &a)
#define rc(a) scanf("%c", &a)
#define rs(a) scanf("%s", a)
#define rb(a) scanf("%lf", &a)
#define rf(a) scanf("%f", &a)
#define pd(a) printf("%d\n", a)
#define plld(a) printf("%lld\n", a)
#define pc(a) printf("%c\n", a)
#define ps(a) printf("%s\n", a)
#define MOD 2018
#define LL long long
#define ULL unsigned long long
#define Pair pair<int, int>
#define mem(a, b) memset(a, b, sizeof(a))
#define _  ios_base::sync_with_stdio(0),cin.tie(0)
//freopen("1.txt", "r", stdin);
using namespace std;
const int maxn = 1e5 + , INF = 0x7fffffff;

int n, m, s, t, k;
int hol[][];
int dir[][] = {{, }, {-, }, {, }, {, -}};

int head[maxn], cur[maxn], d[maxn], nex[maxn << ];
int cnt;

struct node
{
    int u, v, c;
}Node[maxn << ];

void add_(int u, int v, int c)
{
    Node[cnt].u = u;
    Node[cnt].v = v;
    Node[cnt].c = c;
    nex[cnt] = head[u];
    head[u] = cnt++;
}

void add(int u, int v, int c)
{
    add_(u, v, c);
    add_(v, u, );
}

bool bfs()
{
    queue<int> Q;
    mem(d, );
    Q.push(s);
    d[s] = ;
    while(!Q.empty())
    {
        int u = Q.front(); Q.pop();
        for(int i = head[u]; i != -; i = nex[i])
        {
            int v = Node[i].v;
            if(!d[v] && Node[i].c > )
            {
                d[v] = d[u] + ;
                Q.push(v);
                if(v == t) return ;
            }
        }
    }
    return d[t] != ;
}

int dfs(int u, int cap)
{
    int ret = ;
    if(u == t || cap == ) return cap;
    for(int &i = cur[u]; i != -; i = nex[i])
    {
        int v = Node[i].v;
        if(d[v] == d[u] +  && Node[i].c > )
        {
            int V = dfs(v, min(Node[i].c, cap));
            Node[i].c -= V;
            Node[i ^ ].c += V;
            ret += V;
            cap -= V;
            if(cap == ) break;
        }
    }
    if(cap > ) d[u] = -;
    return ret;
}

int Dinic()
{
    int ans = ;
    while(bfs())
    {
        memcpy(cur, head, sizeof head);
        ans += dfs(s, INF);
    }
   return ans;
}

int main()
{
    while(scanf("%d%d%d", &n, &m, &k) != EOF)
    {
        mem(head, -);
        mem(hol, );
        cnt = ;
        s = , t = ;
        int x, y;
        rap(i, , k)
        {
            scanf("%d%d", &y, &x);
            hol[x][y] = ;
        }
        if((n * m - k) & )
        {
            ps("NO");
            continue;
        }
     //   cout << 111 <<endl;
        rap(i, , n)
            rap(j, , m)
            {
                if(hol[i][j]) continue;
                add(s, (i - ) * m + j, );
                add( + (i - ) * m + j, t, );
                rep(q, , )
                {
                    int nx = i + dir[q][];
                    int ny = j + dir[q][];
                    if(nx <  || nx > n || ny <  || ny > m || hol[nx][ny]) continue;
                    add((i - ) * m + j,  + (nx - ) * m + ny, );
                }
            }
       // cout << Dinic() << endl;
      //  cout << n * m
        if(Dinic() == n * m - k)
        {
            ps("YES");
        }
        else
        {
            ps("NO");
        }

    }
    return ;
}