Buggy python submission (verdict: Runtime Error):
import bisect, collections, copy, heapq, itertools, math, string
import sys
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int, sys.stdin.readline().rstrip().split())
def LI(): return list(map(int, sys.stdin.readline().rstrip().split()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
from collections import deque, defaultdict, Counter
import heapq

# SegTreeの関数
def segfunc(x, y):
    return max(x, y)
#区間の最小値、最大値を求めたい、区間の和を求めたいなど。segfuncに関数を書き込んでください。


# 単位元
# min->inf, max->-inf, add->0, mul->1
ide_ele = - float('inf')


# セグメント木
class SegTree:
    """
    init(init_val, segfunc, ide_ele): 配列init_valで初期化、構築
    update(k, x): k番目の値をxに更新
    query(l, r): 区間[l, r)をsegfuncしたものを返す
    """

    def __init__(self, init_val, segfunc, ide_ele):
        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する
        for i in range(n):
            self.tree[self.num + i] = init_val[i]
        # 構築
        for i in range(self.num - 1, 0, -1):
            self.tree[i] = self.segfunc(self.tree[2 * i], self.tree[2 * i + 1])

    def update(self, k, x):
        """
        k番目の値をxに更新
        :param k: index(0-index)
        :param x: update value
        """
        k += self.num
        self.tree[k] = x
        while k > 1:
            self.tree[k >> 1] = self.segfunc(self.tree[k], self.tree[k ^ 1])
            k >>= 1

    def query(self, l, r):
        """
        [l, r)のsegfuncしたものを得る
        :param l: 0-index
        :param r: 0-index
        :return:
        """
        res = self.ide_ele
        l += self.num
        r += self.num
        while l < r:
            if l & 1:
                res = self.segfunc(res, self.tree[l])
                l += 1
            if r & 1:
                res = self.segfunc(res, self.tree[r - 1])
            l >>= 1
            r >>= 1
        return res
def main():
    N, K = MI()
    A = [0] * (3 * 10 ** 5 + 1)
    seg = SegTree(A, segfunc, ide_ele)
    for i in range(N):
        a = I()
        b = seg.query(a - K, a + K + 1)
        seg.update(a, b + 1)
    print(seg.query(1, 3 * 10 ** 5 + 1))
if __name__ == "__main__":
    main()

Fixed submission:
import bisect, collections, copy, heapq, itertools, math, string
import sys
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int, sys.stdin.readline().rstrip().split())
def LI(): return list(map(int, sys.stdin.readline().rstrip().split()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
from collections import deque, defaultdict, Counter
import heapq

# SegTreeの関数
def segfunc(x, y):
    return max(x, y)
#区間の最小値、最大値を求めたい、区間の和を求めたいなど。segfuncに関数を書き込んでください。


# 単位元
# min->inf, max->-inf, add->0, mul->1
ide_ele = - float('inf')


# セグメント木
class SegTree:
    """
    init(init_val, segfunc, ide_ele): 配列init_valで初期化、構築
    update(k, x): k番目の値をxに更新
    query(l, r): 区間[l, r)をsegfuncしたものを返す
    """

    def __init__(self, init_val, segfunc, ide_ele):
        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する
        for i in range(n):
            self.tree[self.num + i] = init_val[i]
        # 構築
        for i in range(self.num - 1, 0, -1):
            self.tree[i] = self.segfunc(self.tree[2 * i], self.tree[2 * i + 1])

    def update(self, k, x):
        """
        k番目の値をxに更新
        :param k: index(0-index)
        :param x: update value
        """
        k += self.num
        self.tree[k] = x
        while k > 1:
            self.tree[k >> 1] = self.segfunc(self.tree[k], self.tree[k ^ 1])
            k >>= 1

    def query(self, l, r):
        """
        [l, r)のsegfuncしたものを得る
        :param l: 0-index
        :param r: 0-index
        :return:
        """
        res = self.ide_ele
        l += self.num
        r += self.num
        while l < r:
            if l & 1:
                res = self.segfunc(res, self.tree[l])
                l += 1
            if r & 1:
                res = self.segfunc(res, self.tree[r - 1])
            l >>= 1
            r >>= 1
        return res
def main():
    N, K = MI()
    A = [0] * (6 * 10 ** 5 + 1)
    seg = SegTree(A, segfunc, ide_ele)
    for i in range(N):
        a = I()
        b = seg.query(max(0, a - K), a + K + 1)
        seg.update(a, b + 1)
    print(seg.query(1, 3 * 10 ** 5 + 1))
if __name__ == "__main__":
    main()