代码一直wa，找不出原因

题目如下：

代码如下：

#include<iostream>
#include<algorithm>
#include<map>
using namespace std;
const int MAX = 500010;
long long arr[MAX], s[MAX], dp[MAX], f[MAX];
map<int, bool>vis;
int main() {
    int n, k;
    cin >> n >> k;
    for (int i = 0; i < n; i++) {
        cin >> arr[i];
        s[arr[i]] ++;  //每个数据计数
    }
    sort(arr, arr + n);  //对序列排序
    int sum = 0;
    if (k == 0) {  //单独讨论k==0的情况
        for (int i = 1; i < n; i++) {
            if (arr[i] != arr[i - 1]) sum++;
        }
        cout << sum + 1 << endl;
        return 0;
    }

    //dp思路是：dp[x] = max(dp[x - k], dp[x - k * 2] + s[x]);将间隔不超过2k的序列链接起来

    for (int i = 0; i < n; i++) {
        if (arr[i] >= k * 2)
            dp[arr[i]] = max(dp[arr[i] - k], dp[arr[i] - k * 2] + s[arr[i]]);
        else if (arr[i] < k) dp[arr[i]] = s[arr[i]];
        else dp[arr[i]] = max(dp[arr[i] - k], s[arr[i]]);
        //cout << dp[arr[i]] << " ";
    }
    if (arr[n - 1] == 0) {  //序列全为0单独讨论
        cout << n << endl;
        return 0;
    }
    for (int i = n - 1; i >= 0; i--) {
        if (s[arr[i] + k] || arr[i] == arr[i + 1]) continue;
        if (!s[arr[i] + k * 2]) {  //如果前面没有链接上类似：n = 6 k = 2 arr为 1 7 9 15 17 21的情况
            sum += dp[arr[i]];
        }
    }
    cout << sum << endl;
    return 0;
}