cf 505c Mr. Kitayuta, the Treasure Hunter

#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>#include <queue>#include <map>#include <vector>using namespace std;const int maxn = 30015;int n, d, vis[maxn], dp[maxn][500];int dfs(int u, int cha){    if (u > 30000) return 0;    if (dp[u][cha] != -1) return dp[u][cha];    int tmp = d + cha - 250;    dp[u][cha] = vis[u];    int ans = 0;    if (tmp > 1)    ans = max(ans, dfs(u + tmp - 1, cha - 1));    ans = max(ans, dfs(u + tmp, cha));    ans = max(ans, dfs(u + tmp + 1, cha + 1));    dp[u][cha] += ans;    return dp[u][cha];}int main(){    scanf("%d%d", &n, &d);    int tmp;    for (int i = 0; i < n; i++)    {        scanf("%d", &tmp);        vis[tmp]++;    }    memset(dp, -1, sizeof(dp));    printf("%d\n", dfs(d, 250));    return 0;}