Why would you use segtree for div3 D? :). I guess you know the approach but simply the idea should be to store the indices of occurence of characters (since there are only 26 of them). And then use binary search to check for all characters if character occurs between [l,r]

Why WA at test 8?

Bcz its wrong

Why on earth would you pass update(1,0,n-1,pos-1,c) when you already did take care of pos as 0-indexed in update function.

Test Case :

rfkqyuqf 10 1 6 y 1 4 n 2 1 2 1 8 r 2 1 6 2 4 7 1 8 v 1 1 l 1 2 p 2 4 6

Expected output : 2 5 3 2

Your output : 2 6 5 5

My submission for reference, even I used segment tree

in update function change pos — 1 to pos

(remove -1 from these line)

char original = arr[pos -1];

arr[pos -1] = val;

290406472 (updated code)

Check my submission for correction.