1638D - Big Brush - CodeForces Solution

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define For(a,x,y) for(int a=x; a<=y; a++)
#define pb push_back
int n,m,a[1010][1010];
struct node{int x,y,val;};
vector<node> ans;
void paint(int x,int y){
	if(x==0||x==n||y==0||y==m) return;
	int val[]={a[x][y],a[x+1][y],a[x][y+1],a[x+1][y+1]};
	sort(val,val+4);
	if(val[3]==0) return;
	bool flag=true;
	For(i,0,2) if(val[i]!=0&&val[i]!=val[3]) flag=false;
	if(!flag) return;
	ans.pb((node){x,y,val[3]});
	For(i,x,x+1) For(j,y,y+1) a[i][j]=0;
	For(i,x-1,x+1) For(j,y-1,y+1) paint(i,j);
}
signed main(){
	cin>>n>>m;
	For(i,1,n) For(j,1,m) cin>>a[i][j];
	For(i,1,n-1) For(j,1,m-1) paint(i,j);
	reverse(ans.begin(),ans.end());
	For(i,1,n) For(j,1,m) if(a[i][j]!=0){cout<<-1<<endl;return 0;}
	cout<<ans.size()<<endl;
	for(auto p:ans) printf("%lld %lld %lld\n",p.x,p.y,p.val);
}