C++(clang++ 11.0.1) 解法, 执行用时: 514ms, 内存消耗: 1144K, 提交时间: 2022-11-28 11:06:30

#include <bits/stdc++.h>
#define rep(i,a,b) for(int i=a;i<=b;i++)
using namespace std;
typedef long long ll;
const int maxn=7000;
const int maxm=100005;
const int inf=0x3f3f3f3f;
int dis[maxn],mp[85][85];
int vis[maxn],pre[maxn];
int head[maxn],cnt;
int n,m,sp,tp;
ll ans=0;
struct node{
    int to,cap,cost,next;
}e[maxm];
void add(int from,int to,int cap,int cost){
    e[cnt].to=to; e[cnt].cap=cap;
    e[cnt].cost=cost; e[cnt].next=head[from];
    head[from]=cnt++;
 
    e[cnt].to=from; e[cnt].cap=0;
    e[cnt].cost=-cost; e[cnt].next=head[to];
    head[to]=cnt++;
}
bool spfa(int s,int t,int &flow,int &cost){
    queue<int> q;
    memset(dis,inf,sizeof(dis));
    memset(vis,0,sizeof(vis));
    memset(pre,-1,sizeof(pre));
    dis[s]=0;  q.push(s);
    vis[s]=1;
    int d=inf;
    while(!q.empty()){
        int u=q.front();
        q.pop();
        vis[u]=0;
        for(int i=head[u];~i;i=e[i].next){
            int v=e[i].to;
            if(e[i].cap>0&&dis[v]>dis[u]+e[i].cost){
                dis[v]=dis[u]+e[i].cost;
                pre[v]=i;
                if(!vis[v]){
                    vis[v]=1;
                    q.push(v);
                }
            }
        }
    }
    if(dis[t]==inf){
        return false;
    }
    for(int i=pre[t];~i;i=pre[e[i^1].to]){
        d=min(d,e[i].cap);
    }
    for(int i=pre[t];~i;i=pre[e[i^1].to]){
        e[i].cap-=d;
        e[i^1].cap+=d;
        cost+=e[i].cost*d;
    }
    flow+=d;
    return true;
}
int mcmf(int s,int t){
    int flow=0,cost=0;
    while(spfa(s,t,flow,cost)){
        //cout<<flow<<" "<<cost<<endl;
    }
    return cost;
}
int G(int x,int y){
    return (x-1)*m+y;
}
int Same(int xl,int yl,int xr,int yr){
    return mp[xl][yl]!=mp[xr][yr];
}
int main(){
    memset(head,-1,sizeof(head));
    ans=0;
    scanf("%d%d",&n,&m);
    sp=0;tp=m*n+1;
    rep(i,1,n) rep(j,1,m) scanf("%d",&mp[i][j]);
 
    rep(i,1,n){
        rep(j,1,m){
            if((i+j)&1){
                add(sp,G(i,j),1,0);
                if(i>1) add(G(i,j),G(i-1,j),1,Same(i,j,i-1,j));
                if(j>1) add(G(i,j),G(i,j-1),1,Same(i,j,i,j-1));
                if(j<m) add(G(i,j),G(i,j+1),1,Same(i,j,i,j+1));
                if(i<n) add(G(i,j),G(i+1,j),1,Same(i,j,i+1,j));
            }
            else add(G(i,j),tp,1,0);
        }
    }
 
    cout<<mcmf(sp,tp)<<endl;
 
    return 0;
}