Problem p02537 (python)

Fixed submission:
class LazySegmentTree:
    def __init__(self, data, default=0, func=max):
        """initialize the lazy segment tree with data"""
        self._default = default
        self._func = func

        self._len = len(data)
        self._size = _size = 1 << (self._len - 1).bit_length()
        self._lazy = [0] * (2 * _size)

        self.data = [default] * (2 * _size)
        self.data[_size:_size + self._len] = data
        for i in reversed(range(_size)):
            self.data[i] = func(self.data[i + i], self.data[i + i + 1])

    def __len__(self):
        return self._len

    def _push(self, idx):
        """push query on idx to its children"""
        # Let the children know of the queries
        q, self._lazy[idx] = self._lazy[idx], 0

        if q:
            self._lazy[2 * idx] = max(self._lazy[2 * idx],q)
            self._lazy[2 * idx + 1] = max(self._lazy[2 * idx + 1],q)
            self.data[2 * idx] = max(self.data[2 * idx], q)
            self.data[2 * idx + 1] = max(self.data[2 * idx + 1], q)

    def _update(self, idx):
        """updates the node idx to know of all queries applied to it via its ancestors"""
        for i in reversed(range(1, idx.bit_length())):
            self._push(idx >> i)

    def _build(self, idx):
        """make the changes to idx be known to its ancestors"""
        idx >>= 1
        while idx:
            self.data[idx] = max(self.data[idx], self._func(self.data[2 * idx], self.data[2 * idx + 1]))
            self._push(idx)
            idx >>= 1

    def add(self, start, stop, value):
        """lazily add value to [start, stop)"""
        start = start_copy = start + self._size
        stop = stop_copy = stop + self._size
        while start < stop:
            #print('a', start, stop)
            if start & 1:
                self._lazy[start] = max(self._lazy[start], value)
                self.data[start] = max(self.data[start],value)
                start += 1
            if stop & 1:
                stop -= 1
                self._lazy[stop] = max(self._lazy[stop], value)
                self.data[stop] = max(self.data[stop],value)
            start >>= 1
            stop >>= 1

        # Tell all nodes above of the updated area of the updates
        self._build(start_copy)
        self._build(stop_copy - 1)

    def query(self, start, stop, default=0):
        """func of data[start, stop)"""
        start += self._size
        stop += self._size

        # Apply all the lazily stored queries
        self._update(start)
        self._update(stop - 1)

        res = default
        while start < stop:
            if start & 1:
                res = self._func(res, self.data[start])
                start += 1
            if stop & 1:
                stop -= 1
                res = self._func(res, self.data[stop])
            start >>= 1
            stop >>= 1
        return res

    def __repr__(self):
        return "LazySegmentTree({0})".format(self.data)

import sys
input = sys.stdin.readline

n, k = map(int, input().split())
seg = LazySegmentTree([0] * (1 << 20))
for _ in range(n):
    v = int(input())
    most = seg.query(v, v+1)
    #print(most)
    seg.add(max(0,v - k), v + k + 1, most + 1)
    #print(seg.data)
print(seg.query(0, 1 << 20))

Buggy submission (verdict: Runtime Error):
class LazySegmentTree:
    def __init__(self, data, default=0, func=max):
        """initialize the lazy segment tree with data"""
        self._default = default
        self._func = func

        self._len = len(data)
        self._size = _size = 1 << (self._len - 1).bit_length()
        self._lazy = [0] * (2 * _size)

        self.data = [default] * (2 * _size)
        self.data[_size:_size + self._len] = data
        for i in reversed(range(_size)):
            self.data[i] = func(self.data[i + i], self.data[i + i + 1])

    def __len__(self):
        return self._len

    def _push(self, idx):
        """push query on idx to its children"""
        # Let the children know of the queries
        q, self._lazy[idx] = self._lazy[idx], 0

        if q:
            self._lazy[2 * idx] = max(self._lazy[2 * idx],q)
            self._lazy[2 * idx + 1] = max(self._lazy[2 * idx + 1],q)
            self.data[2 * idx] = max(self.data[2 * idx], q)
            self.data[2 * idx + 1] = max(self.data[2 * idx + 1], q)

    def _update(self, idx):
        """updates the node idx to know of all queries applied to it via its ancestors"""
        for i in reversed(range(1, idx.bit_length())):
            self._push(idx >> i)

    def _build(self, idx):
        """make the changes to idx be known to its ancestors"""
        idx >>= 1
        while idx:
            self.data[idx] = max(self.data[idx], self._func(self.data[2 * idx], self.data[2 * idx + 1]))
            self._push(idx)
            idx >>= 1

    def add(self, start, stop, value):
        """lazily add value to [start, stop)"""
        start = start_copy = start + self._size
        stop = stop_copy = stop + self._size
        while start < stop:
            #print('a', start, stop)
            if start & 1:
                self._lazy[start] = max(self._lazy[start], value)
                self.data[start] = max(self.data[start],value)
                start += 1
            if stop & 1:
                stop -= 1
                self._lazy[stop] = max(self._lazy[stop], value)
                self.data[stop] = max(self.data[stop],value)
            start >>= 1
            stop >>= 1

        # Tell all nodes above of the updated area of the updates
        self._build(start_copy)
        self._build(stop_copy - 1)

    def query(self, start, stop, default=0):
        """func of data[start, stop)"""
        start += self._size
        stop += self._size

        # Apply all the lazily stored queries
        self._update(start)
        self._update(stop - 1)

        res = default
        while start < stop:
            if start & 1:
                res = self._func(res, self.data[start])
                start += 1
            if stop & 1:
                stop -= 1
                res = self._func(res, self.data[stop])
            start >>= 1
            stop >>= 1
        return res

    def __repr__(self):
        return "LazySegmentTree({0})".format(self.data)

import sys
input = sys.stdin.readline

n, k = map(int, input().split())
seg = LazySegmentTree([0] * (65536))
for _ in range(n):
    v = int(input())
    most = seg.query(v, v+1)
    #print(most)
    seg.add(max(0,v - k), v + k + 1, most + 1)
    #print(seg.data)
print(seg.query(0, 65536))