Problem:
Score : 500 points

Problem Statement

You are given a string S of length N consisting of lowercase English letters.

Process Q queries of the following two types:

Type 1: change the i_q-th character of S to c_q. (Do nothing if the i_q-th character is already c_q.)

Type 2: answer the number of different characters occurring in the substring of S between the l_q-th and r_q-th characters (inclusive).

Constraints

N, Q, i_q, l_q, and r_q are integers.

S is a string consisting of lowercase English letters.

c_q is a lowercase English letter.

1 \leq N \leq 500000

1 \leq Q \leq 20000

|S| = N

1 \leq i_q \leq N

1 \leq l_q \leq r_q \leq N

There is at least one query of type 2 in each testcase.

Input

Input is given from Standard Input in the following format:

N
S
Q
Query_1
\vdots
Query_Q

Here, Query_i in the 4-th through (Q+3)-th lines is one of the following:

1 i_q c_q

2 l_q r_q

Output

For each query of type 2, print a line containing the answer.

Sample Input 1

7
abcdbbd
6
2 3 6
1 5 z
2 1 1
1 4 a
1 7 d
2 1 7

Sample Output 1

3
1
5

In the first query, cdbb contains three kinds of letters: b , c , and d, so we print 3.

In the second query, S is modified to abcdzbd.

In the third query, a contains one kind of letter: a, so we print 1.

In the fourth query, S is modified to abcazbd.

In the fifth query, S does not change and is still abcazbd.

In the sixth query, abcazbd contains five kinds of letters: a, b, c, d, and z, so we print 5.

Solution in Kotlin (1.3.71) (judge verdict: Runtime Error)

import java.io.BufferedReader
import java.io.InputStreamReader
import java.io.PrintWriter
import java.util.*
import kotlin.math.abs
import kotlin.math.cos
import kotlin.math.max
import kotlin.math.min

val br = BufferedReader(InputStreamReader(System.`in`))
val out = PrintWriter(System.out)

fun main() {
    br.use { out.use {
        solve()
        out.flush()
    } }
}

fun solve() {
    val n = readInteger()
    val s = br.readLine()!!.toCharArray()
    val q = readInteger()

    val segTree = SegmentTree(s.size)
    for ((i, c) in s.withIndex()) {
        segTree.update(i, c)
    }

    repeat(q) {
        val (a, i, c) = readStringList()
        if (a == "1") {
            segTree.update(i.toInt() - 1, c[0])
        } else {
            val l = i.toInt() - 1
            val r = c.toInt()
            val v = segTree.query(l, r)
//            segTree.debug()
//            out.println()
            out.println(v.size)

        }
    }
}

class SegmentTree(private val length: Int) {
    val tree = Array(capacity(length)) { emptySet<Char>() }

    fun debug() {
        for ((v, i ) in tree.withIndex()) {
            out.println(v to i)
            if (v in listOf(0, 2, 6, 14)) out.println()
        }
    }

    fun update(i: Int, v: Char) {
        var nodeIndex = tree.size - length + i - 1
        tree[nodeIndex] = setOf(v)
        while (nodeIndex > 0) {
            nodeIndex = (nodeIndex - 1) / 2
            val a = tree[nodeIndex * 2 + 1]
            val b = tree[nodeIndex * 2 + 2]
            tree[nodeIndex] = a union b
        }
    }

    fun query(l: Int, r: Int, nodeIndex: Int = 0, currentL: Int = 0, currentR: Int = (capacity(length) + 1) / 2): Set<Char> {
        if (currentR <= l || r <= currentL) return emptySet()
        if (l <= currentL &&  currentR <= r)  {
//            out.println(nodeIndex)
            return tree[nodeIndex]
        }
        val a = query(l, r, nodeIndex * 2 + 1, currentL, (currentL + currentR) / 2)
        val b = query(l, r, nodeIndex * 2 + 2, (currentL + currentR) / 2, currentR)
        return a union b
    }

    fun capacity(length: Int): Int {
        var ans = 2
        while (ans < length * 2 - 1) ans *= 2
        return ans - 1
    }
}

fun readInteger() = Integer.parseInt(br.readLine())
fun readLong() = java.lang.Long.parseLong(br.readLine())
fun readStringList() = br.readLine()!!.split(' ')
fun readIntegerList() = readStringList().map(Integer::parseInt)
fun readLongList() = readStringList().map(java.lang.Long::parseLong)
fun readDoubleList() = readStringList().map(java.lang.Double::parseDouble)