AcWing 901. 滑雪

//f[i][j]表示从(i,j)开始滑的路径
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int N = 310;
int n, m;
int g[N][N];
int f[N][N];
int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};
int dp(int x, int y) {
    int &v = f[x][y];
    if (v != -1) return v;
    v = 1;//加上*之后，这里等价f[x][y]=1;   (引用) 
    for (int i = 0; i < 4; i ++ ) {
        int a = x + dx[i], b = y + dy[i];
        if (a >= 1 && a <= n && b >= 1 && b <= m && g[x][y] > g[a][b])
            v = max(v, dp(a, b) + 1);
    }
    return v;
}
int main() {
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= n; i ++ )
        for (int j = 1; j <= m; j ++ )
            scanf("%d", &g[i][j]);
    memset(f, -1, sizeof f);//表示每个状态都没算过 
    int res = 0;
    for (int i = 1; i <= n; i ++ )
        for (int j = 1; j <= m; j ++ )
            res = max(res, dp(i, j));
    printf("%d
", res);
    return 0;
}