알고리즘 92 :: BOJ_내리막길(DFS, DP) [진행중]

package backjun;
 
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.StringTokenizer;
 
public class backjun_1520_내리막길 {
 
    private static int column; 
    private static int row;
    private static int[] dx = {-1,1,0,0};
    private static int[] dy = {0,0,-1,1};
    private static int[][] map;
    private static int answer;
    static void DFS(int nn) {
        
        int x = nn/column;
        int y = nn%column;
        if(x==row-1 && y==column-1) {
            answer+=1;
        }
        int beforeValue = map[x][y];
        for(int i=0; i<4; i++) {
            int ddx = x + dx[i];
            int ddy = y + dy[i];
            //은행 라이브 몇시지
            if(ddx<0 || ddx>=row || ddy<0 || ddy>=column) continue;
            else {
                int afterValue = map[ddx][ddy];
                if(beforeValue>afterValue)
                    DFS(ddx*column+ddy);
            }
            
        }
        
        
    }
    public static void main(String[] args) throws Exception{
        // TODO Auto-generated method stub
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());
        int n = Integer.parseInt(st.nextToken());
        int m = Integer.parseInt(st.nextToken());
        
        column = m;
        row = n;
        
        map = new int[n][m];
        for(int i=0; i<n; i++) {
            st = new StringTokenizer(br.readLine());
            for(int j=0; j<m; j++) {
                map[i][j] = Integer.parseInt(st.nextToken());
            }
        }//end of for loop
        
        //end of sysout
        
        DFS(0);
        System.out.println(answer);
        
    }
 
}
 

시간초과가 난다. 어떻게 해결할 수 있을까?