Buggy python submission (verdict: Runtime Error):
# 0-index segment tree


class SegmentTree:
    """
    init(init_val, ide_ele): 配列init_valで初期化  O(N)
    update(k, x): k番目の値をxに更新                O(logN)
    query(l, r): 区間[l, r)をsegfuncしたものを返す   O(logN)
    """

    def __init__(self, init_val, segfunc, ide_ele):
        """
        init_val: 配列の初期値
        segfunc: 区間にしたい操作
        ide_ele: 単位元
        n: 要素数
        num: n以上の最小の2のべき乗
        tree: セグメント木(0-index)
        """
        n = len(init_val)
        self.segfunc = segfunc
        self.ide_ele = ide_ele
        self.num = 1 << (n - 1).bit_length()
        self.tree = [ide_ele] * 2 * self.num
        # 配列の値を葉にセット
        for i in range(n):
            self.tree[self.num - 1 + i] = init_val[i]
        # 構築していく
        for i in range(self.num - 2, -1, -1):
            self.tree[i] = self.segfunc(self.tree[2 * i + 1], self.tree[2 * i + 2])

    def update(self, k, x):
        """
        k番目の値をxに更新
        k: index(0-index)
        x: update value
        """
        k += self.num - 1
        # self.tree[k]  = x   <- when updated
        # self.tree[k] += x  <- when added
        self.tree[k] = x
        while k > 0:
            k = (k - 1) // 2
            self.tree[k] = self.segfunc(self.tree[2 * k + 1], self.tree[2 * k + 2])

    def query(self, left, right):

        if left >= right:
            print("left must be smaller than right")
            exit(0)

        if right > self.num:
            print("right must be smaller than self.num")
            exit(0)

        """
        [l, r)のsegfuncしたものを得る
        l: index(0-index)
        r: index(0-index)
        """
        res = self.ide_ele

        left += self.num - 1
        right += self.num - 1
        while left < right:
            if left & 1 == 0:
                res = self.segfunc(res, self.tree[left])
            if right & 1 == 0:
                right -= 1
                res = self.segfunc(res, self.tree[right])
            left >>= 1
            right >>= 1
        return res


MAX_NUM = 10
n, k = map(int, input().split())

a = []
for i in range(n):
    a.append(int(input()))

dp = [0] * (MAX_NUM + 5)

segfunc = max
ide_ele = -float("inf")

st = SegmentTree(dp, segfunc, ide_ele)

for num in a:
    left = max(0, num - k)
    right = min(MAX_NUM, num + k) + 1

    st.update(num, st.query(left, right) + 1)

print(st.query(0, MAX_NUM + 1))


Fixed submission:
# 0-index segment tree


class SegmentTree:
    """
    init(init_val, ide_ele): 配列init_valで初期化  O(N)
    update(k, x): k番目の値をxに更新                O(logN)
    query(l, r): 区間[l, r)をsegfuncしたものを返す   O(logN)
    """

    def __init__(self, init_val, segfunc, ide_ele):
        """
        init_val: 配列の初期値
        segfunc: 区間にしたい操作
        ide_ele: 単位元
        n: 要素数
        num: n以上の最小の2のべき乗
        tree: セグメント木(0-index)
        """
        n = len(init_val)
        self.segfunc = segfunc
        self.ide_ele = ide_ele
        self.num = 1 << (n - 1).bit_length()
        self.tree = [ide_ele] * 2 * self.num
        # 配列の値を葉にセット
        for i in range(n):
            self.tree[self.num - 1 + i] = init_val[i]
        # 構築していく
        for i in range(self.num - 2, -1, -1):
            self.tree[i] = self.segfunc(self.tree[2 * i + 1], self.tree[2 * i + 2])

    def update(self, k, x):
        """
        k番目の値をxに更新
        k: index(0-index)
        x: update value
        """
        k += self.num - 1
        # self.tree[k]  = x   <- when updated
        # self.tree[k] += x  <- when added
        self.tree[k] = x
        while k > 0:
            k = (k - 1) // 2
            self.tree[k] = self.segfunc(self.tree[2 * k + 1], self.tree[2 * k + 2])

    def query(self, left, right):

        if left >= right:
            print("left must be smaller than right")
            exit(0)

        if right > self.num:
            print("right must be smaller than self.num")
            exit(0)

        """
        [l, r)のsegfuncしたものを得る
        l: index(0-index)
        r: index(0-index)
        """
        res = self.ide_ele

        left += self.num - 1
        right += self.num - 1
        while left < right:
            if left & 1 == 0:
                res = self.segfunc(res, self.tree[left])
            if right & 1 == 0:
                right -= 1
                res = self.segfunc(res, self.tree[right])
            left >>= 1
            right >>= 1
        return res


MAX_NUM = 300000
n, k = map(int, input().split())

a = []
for i in range(n):
    a.append(int(input()))

dp = [0] * (MAX_NUM + 5)

segfunc = max
ide_ele = -float("inf")

st = SegmentTree(dp, segfunc, ide_ele)

for num in a:
    left = max(0, num - k)
    right = min(MAX_NUM, num + k) + 1

    st.update(num, st.query(left, right) + 1)

print(st.query(0, MAX_NUM + 1))