Buggy python submission (verdict: Time Limit Exceeded):
class SegmentTree:
    _op = None
    _e = None
    _size = None
    _offset = None
    _data = None

    def __init__(self, size, op, e):
        self._op = op
        self._e = e
        self._size = size
        t = 1
        while t < size:
            t *= 2
        self._offset = t - 1
        self._data = [0] * (t * 2 - 1)

    def build(self, iterable):
        op = self._op
        data = self._data
        data[self._offset:self._offset + self._size] = iterable
        for i in range(self._offset - 1, -1, -1):
            data[i] = op(data[i * 2 + 1], data[i * 2 + 2])

    def update(self, index, value):
        op = self._op
        data = self._data
        i = self._offset + index
        data[i] = value
        while i >= 1:
            i = (i - 1) // 2
            data[i] = op(data[i * 2 + 1], data[i * 2 + 2])

    def query(self, start, stop):
        def iter_segments(data, l, r):
            while l < r:
                if l & 1 == 0:
                    yield data[l]
                if r & 1 == 0:
                    yield data[r - 1]
                l = l // 2
                r = (r - 1) // 2
        op = self._op
        it = iter_segments(self._data, start + self._offset,
                           stop + self._offset)
        result = self._e
        for v in it:
            result = op(result, v)
        return result


N, K, *A = map(int, open(0).read().split())
st = SegmentTree(300000 + 1, max, 0)

for a in A:
    st.update(a, st.query(max(a - K, 0), min(a + K + 1, 300000 + 1)) + 1)

print(st.query(0, 300000 + 1))


Fixed submission:
class SegmentTree:
    _op = None
    _e = None
    _size = None
    _offset = None
    _data = None

    def __init__(self, size, op, e):
        self._op = op
        self._e = e
        self._size = size
        t = 1
        while t < size:
            t *= 2
        self._offset = t - 1
        self._data = [0] * (t * 2 - 1)

    def build(self, iterable):
        op = self._op
        data = self._data
        data[self._offset:self._offset + self._size] = iterable
        for i in range(self._offset - 1, -1, -1):
            data[i] = op(data[i * 2 + 1], data[i * 2 + 2])

    def update(self, index, value):
        op = self._op
        data = self._data
        i = self._offset + index
        data[i] = value
        while i >= 1:
            i = (i - 1) // 2
            data[i] = op(data[i * 2 + 1], data[i * 2 + 2])

    def query(self, start, stop):
        def iter_segments(data, l, r):
            while l < r:
                if l & 1 == 0:
                    yield data[l]
                if r & 1 == 0:
                    yield data[r - 1]
                l = l // 2
                r = (r - 1) // 2
        op = self._op
        it = iter_segments(self._data, start + self._offset,
                           stop + self._offset)
        result = self._e
        for v in it:
            result = op(result, v)
        return result


N, K, *A = map(int, open(0).read().split())
st = SegmentTree(300000 + 1, max, 0)

for a in A:
    st.update(a, st.query(max(a - K, 0), min(a + K + 1, 300000 + 1)) + 1)

print(st.query(0, 300000 + 1))

Buggy python submission (verdict: Runtime Error):
package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func min(x, y int) int {
	if x < y {
		return x
	}
	return y
}

func max(x, y int) int {
	if x > y {
		return x
	}
	return y
}

type segmentTree struct {
	offset int
	data   []int
	op     func(x, y int) int
	e      int
}

func newSegmentTree(n int, op func(x, y int) int, e int) segmentTree {
	var result segmentTree
	t := 1
	for t < n {
		t *= 2
	}
	result.offset = t - 1
	result.data = make([]int, 2*t-1)
	for i := 0; i < len(result.data); i++ {
		result.data[i] = e
	}
	result.op = op
	result.e = e
	return result
}

func (st segmentTree) build(a []int) {
	for i, v := range a {
		st.data[st.offset+i] = v
	}
	for i := st.offset - 1; i > -1; i-- {
		st.data[i] = st.op(st.data[i*2+1], st.data[i*2+2])
	}
}

func (st segmentTree) get(index int) int {
	return st.data[st.offset+index]
}

func (st segmentTree) update(index, value int) {
	i := st.offset + index
	st.data[i] = value
	for i >= 1 {
		i = (i - 1) / 2
		st.data[i] = st.op(st.data[i*2+1], st.data[i*2+2])
	}
}

func (st segmentTree) query(start, stop int) int {
	result := st.e
	l := start + st.offset
	r := stop + st.offset
	for l < r {
		if l&1 == 0 {
			result = st.op(result, st.data[l])
		}
		if r&1 == 0 {
			result = st.op(result, st.data[r-1])
		}
		l = l / 2
		r = (r - 1) / 2
	}
	return result
}

func main() {
	defer flush()

	N := readInt()
	K := readInt()

	A := make([]int, N)
	for i := 0; i < N; i++ {
		A[i] = readInt()
	}

	st := newSegmentTree(300000+1, max, 0)

	t := make([]int, N)
	result := 0
	for i := 0; i < N; i++ {
		t[i] = st.query(max(A[i]-K, 0), min(A[i]+K+1, 300000+1)) + 1
		result = max(result, t[i])
		st.update(A[i], t[i])
	}
	println(result)
}

const (
	ioBufferSize = 1 * 1024 * 1024 // 1 MB
)

var stdinScanner = func() *bufio.Scanner {
	result := bufio.NewScanner(os.Stdin)
	result.Buffer(make([]byte, ioBufferSize), ioBufferSize)
	result.Split(bufio.ScanWords)
	return result
}()

func readString() string {
	stdinScanner.Scan()
	return stdinScanner.Text()
}

func readInt() int {
	result, err := strconv.Atoi(readString())
	if err != nil {
		panic(err)
	}
	return result
}

var stdoutWriter = bufio.NewWriter(os.Stdout)

func flush() {
	stdoutWriter.Flush()
}

func println(args ...interface{}) (int, error) {
	return fmt.Fprintln(stdoutWriter, args...)
}


Fixed submission:
class SegmentTree:
    _op = None
    _e = None
    _size = None
    _offset = None
    _data = None

    def __init__(self, size, op, e):
        self._op = op
        self._e = e
        self._size = size
        t = 1
        while t < size:
            t *= 2
        self._offset = t - 1
        self._data = [0] * (t * 2 - 1)

    def build(self, iterable):
        op = self._op
        data = self._data
        data[self._offset:self._offset + self._size] = iterable
        for i in range(self._offset - 1, -1, -1):
            data[i] = op(data[i * 2 + 1], data[i * 2 + 2])

    def update(self, index, value):
        op = self._op
        data = self._data
        i = self._offset + index
        data[i] = value
        while i >= 1:
            i = (i - 1) // 2
            data[i] = op(data[i * 2 + 1], data[i * 2 + 2])

    def query(self, start, stop):
        def iter_segments(data, l, r):
            while l < r:
                if l & 1 == 0:
                    yield data[l]
                if r & 1 == 0:
                    yield data[r - 1]
                l = l // 2
                r = (r - 1) // 2
        op = self._op
        it = iter_segments(self._data, start + self._offset,
                           stop + self._offset)
        result = self._e
        for v in it:
            result = op(result, v)
        return result


N, K, *A = map(int, open(0).read().split())
st = SegmentTree(300000 + 1, max, 0)

for a in A:
    st.update(a, st.query(max(a - K, 0), min(a + K + 1, 300000 + 1)) + 1)

print(st.query(0, 300000 + 1))