Buggy python submission (verdict: Runtime Error):
#####segfunc#####
def segfunc(x, y):
  return max(x,y)
#################

#####ide_ele#####
ide_ele = 0
#################

class SegTree:
  """
  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(1-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 + i] = init_val[i]
    # 構築していく
    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
    k: index(0-index)
    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
    l: index(0-index)
    r: index(0-index)
    """
    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 = map(int, input().split())
  a = []
  for i in range(n):
    a.append(int(input())-1)

  array = [0] * n
  seg = SegTree(array, segfunc, ide_ele)
  non_select = [0] * n
  select = [0] * n
  select[0] = a[0]
  seg.update(a[0], 1)

  for i in range(1, len(a)):
    low = max(0, a[i] - k)
    high = min(a[i] + k + 1, n)
    tmp = seg.query(low, high) + 1
    
    seg.update(a[i], tmp)
    
  print(seg.query(0, n))
  
main()

Fixed submission:
#####segfunc#####
def segfunc(x, y):
  return max(x,y)
#################

#####ide_ele#####
ide_ele = 0
#################

class SegTree:
  """
  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(1-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 + i] = init_val[i]
    # 構築していく
    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
    k: index(0-index)
    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
    l: index(0-index)
    r: index(0-index)
    """
    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 = map(int, input().split())
  a = []
  for i in range(n):
    a.append(int(input()))

  array = [0] * (3 * (10 ** 5) + 1)
  seg = SegTree(array, segfunc, ide_ele)

  for i in range(len(a)):
    low = max(0, a[i] - k)
    high = min(a[i] + k + 1, 3 * (10 ** 5) + 1)
    tmp = seg.query(low, high) + 1
    
    seg.update(a[i], tmp)
    
  print(seg.query(0, 3 * (10 ** 5) + 1))
  
main()

Buggy python submission (verdict: Runtime Error):
#####segfunc#####
def segfunc(x, y):
  return max(x,y)
#################

#####ide_ele#####
ide_ele = 0
#################

class SegTree:
  """
  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(1-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 + i] = init_val[i]
    # 構築していく
    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
    k: index(0-index)
    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
    l: index(0-index)
    r: index(0-index)
    """
    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 = map(int, input().split())
  a = []
  for i in range(n):
    a.append(int(input()))

  array = [0] * n
  seg = SegTree(array, segfunc, ide_ele)
  non_select = [0] * n
  select = [0] * n
  select[0] = a[0]
  seg.update(a[0], 1)

  for i in range(1, len(a)):
    low = max(0, a[i] - k)
    high = min(a[i] + k + 1, n)
    tmp = seg.query(low, high) + 1
    
    seg.update(a[i], tmp)
    
  print(seg.query(0, n))
  
main()

Fixed submission:
#####segfunc#####
def segfunc(x, y):
  return max(x,y)
#################

#####ide_ele#####
ide_ele = 0
#################

class SegTree:
  """
  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(1-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 + i] = init_val[i]
    # 構築していく
    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
    k: index(0-index)
    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
    l: index(0-index)
    r: index(0-index)
    """
    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 = map(int, input().split())
  a = []
  for i in range(n):
    a.append(int(input()))

  array = [0] * (3 * (10 ** 5) + 1)
  seg = SegTree(array, segfunc, ide_ele)

  for i in range(len(a)):
    low = max(0, a[i] - k)
    high = min(a[i] + k + 1, 3 * (10 ** 5) + 1)
    tmp = seg.query(low, high) + 1
    
    seg.update(a[i], tmp)
    
  print(seg.query(0, 3 * (10 ** 5) + 1))
  
main()