40pts求调

#include<bits/stdc++.h>
#define ll long long 
#define N 1010
using namespace std;
ll n,m,lx,ly,Max,ans;
ll a[N][N],f[N][N];
ll bj[N][N];
ll dx[4]={0,0,1,-1};
ll dy[4]={1,-1,0,0};
void dfs(ll x,ll y){
	for(int i=0;i<4;i++){
		ll nx=x+dx[i],ny=y+dy[i];
		if(nx<1||nx>n||ny<1||ny>m||bj[nx][ny])continue;			
		if(a[nx][ny]>a[x][y])continue;
		if(f[nx][ny]>f[x][y]+1)continue;
		bj[nx][ny]=1;
		f[nx][ny]=f[x][y]+1;
		dfs(nx,ny);
		bj[nx][ny]=0;
	}
}

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0),cout.tie(0);
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			cin>>a[i][j];
			if(a[i][j]>Max){
				Max=a[i][j];
				lx=i,ly=j;
			}
		}
	}
	f[lx][ly]=1;
	bj[lx][ly]=1;
	dfs(lx,ly);	
	for(int i=1;i<=n;i++)
		for(int j=1;j<=m;j++)
			ans=max(ans,f[i][j]);
	cout<<ans<<"\n";
	return 0;
}