​​http://codeforces.com/contest/1638/problem/D​​

按题意着色则需要考虑先后次序问题，次序问题一般用拓扑解决。

#include <bits/stdc++.h>
using namespace std;
const int maxn=1e3+10;

struct node
{
    int x,y,c;
};

queue <node> que;
node ans[maxn*maxn];
int ary[maxn][maxn],book[maxn][maxn],col[maxn*maxn];
int n,m,len;

int judge(int x,int y)
{
    int i,j,tx,ty,cnt,zero,syt;
    cnt=0,zero=0,syt=1;
    for(i=0;i<=1;i++){
        for(j=0;j<=1;j++){
            if(!col[ary[x+i][y+j]]){
                col[ary[x+i][y+j]]=1;
                cnt++;
                if(ary[x+i][y+j]==0){
                    zero=1;
                }
                else{
                    syt=ary[x+i][y+j];
                }
            }
        }
    }
    for(i=0;i<=1;i++){
        for(j=0;j<=1;j++){
            col[ary[x+i][y+j]]=0;
        }
    }
    if(cnt==1||cnt==2&&zero){
        return syt;
    }
    else{
        return -1;
    }
}

bool toposort()
{
    node cur,tmp;
    int i,j,k,cnt,res;
    len=0;
    for(i=1;i<=n-1;i++){
        for(j=1;j<=m-1;j++){
            if(ary[i][j]==ary[i+1][j]&&ary[i][j]==ary[i][j+1]&&ary[i][j]==ary[i+1][j+1]){
                tmp.x=i,tmp.y=j,tmp.c=ary[i][j];
                que.push(tmp);
                book[tmp.x][tmp.y]=1;
                len++;
                ans[len]=tmp;
            }
        }
    }
    while(!que.empty()){
        cur=que.front();
        que.pop();
        ary[cur.x][cur.y]=0,ary[cur.x+1][cur.y]=0,ary[cur.x][cur.y+1]=0,ary[cur.x+1][cur.y+1]=0;
        //printf("%d %d %d\n",cur.x,cur.y,cur.c);
        for(i=-1;i<=1;i++){
            for(j=-1;j<=1;j++){
                tmp.x=cur.x+i,tmp.y=cur.y+j;
                if(tmp.x<1||tmp.x+1>n||tmp.y<1||tmp.y+1>m){
                    continue;
                }
                res=judge(tmp.x,tmp.y);
                if(!book[tmp.x][tmp.y]&&res!=-1){
                    tmp.c=res;
                    que.push(tmp);
                    book[tmp.x][tmp.y]=1;
                    len++;
                    ans[len]=tmp;
                }
            }
        }
    }
    memset(book,0,sizeof(book));
    cnt=0;
    for(k=1;k<=len;k++){
        for(i=0;i<=1;i++){
            for(j=0;j<=1;j++){
                if(!book[ans[k].x+i][ans[k].y+j]){
                    book[ans[k].x+i][ans[k].y+j]=1;
                    cnt++;
                }
            }
        }
    }
    return cnt==n*m;
}

int main()
{
    int i,j;
    scanf("%d%d",&n,&m);
    for(i=1;i<=n;i++){
        for(j=1;j<=m;j++){
            scanf("%d",&ary[i][j]);
        }
    }
    if(toposort()){
        printf("%d\n",len);
        for(i=len;i>=1;i--){
            printf("%d %d %d\n",ans[i].x,ans[i].y,ans[i].c);
        }
    }
    else{
        printf("-1\n");
    }


    return 0;
}