[백준] 1520 내리막길

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import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.StringTokenizer;

public class Main {
	static int T, N,M;
	static int arr[][], dp[][], delta[][] = {{1,0},{0,1},{0,-1},{-1,0}};
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); 
		StringTokenizer st = new StringTokenizer(br.readLine()); //n,m input
		N = Integer.parseInt(st.nextToken());
		M = Integer.parseInt(st.nextToken());
		arr = new int[N][M]; // 산 배열 
		dp = new int[N][M];
		
		for (int i = 0; i < N; i++) { // 라인 별로 받아 산 배열 받기
			st = new StringTokenizer(br.readLine());
			for (int j = 0; j < M; j++) {
				arr[i][j] = Integer.parseInt(st.nextToken());
			}
		}
		for (int i = 0; i < N; i++) {
			Arrays.fill(dp[i], -1);
		}
		System.out.println(dfs(0,0));
	}
	
	public static int dfs(int x, int y) {
        if (x == N - 1 && y == M - 1) return 1;     //재귀 탈출조건
        if (dp[x][y] != -1) return dp[x][y];
        dp[x][y] = 0; //방문처리
        for (int i = 0; i < 4; i++) {
            int nx = x + delta[i][0];
            int ny = y + delta[i][1];
            if (nx < 0 || nx >= N || ny < 0 || ny >= M) continue;
            if(arr[x][y] > arr[nx][ny]) {
                dp[x][y] += dfs(nx, ny); 가지수가 이전꺼에 더해짐
            }
        }
        return dp[x][y];
    }

}