I’m new to working on segtrees and i needed to solve a problem where i find the first value > x in a certain range.
I’ve been using the recursive method to create the segtree and to update it, but i wasn’t able to retrieve the index of the first value > x in my range.

I’ll paste all of my code here in case it can help:

//THIS IS THE GRADER, IGNORE UNTIL THE SOLUTION PART -------------------------------------
#include <utility>
#include <iostream>
#include <vector>
using namespace std;

// Declaring variables
static int R;
static vector<int> risultato1;
static vector<int> risultato2;

// Declaring functions
void inizializza(int N, vector<int> H);

// Functions ad-hoc for this grader
pair<int, int> chiedi(int x);
void cambia(int x, int h);

void leggi_eventi(int M) {
    for (int i = 0; i < M; i++) {
        char tipo;
        cin >> tipo;

        if (tipo == 'Q') {
            int x;
            cin >> x;
            pair<int, int> risultato = chiedi(x);
            risultato1[R] = risultato.first;
            risultato2[R] = risultato.second;
            R++;
        } else {
            int x, h;
            cin >> x >> h;
            cambia(x, h);
        }
    }
}


int main() {

    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    // Reading input
    int N, M;
    cin >> N >> M;

    vector<int> H(N);
    risultato1.resize(M);
    risultato2.resize(M);

    for (int i = 0; i < N; i++) {
        cin >> H[i];
    }

    // Calling functions
    inizializza(N, H);
    leggi_eventi(M);

    // Writing output
    for (int i = 0; i < R; i++) {
        cout << risultato1[i] << ' ' << risultato2[i] << 'n';
    }

    return 0;
}




//SOLUTION-------------------------------------------------------------------------------

//SEGMENT TREE
vector<int> seg;
vector<int> torre;
int sizeN;

//recursive build of the segtree
long long int build(int i, int l, int r, vector<int> &torri) {

    if(r-l==1) return seg[i] = torri[l]; //base case

    int mid = (l+r)/2; //split in half
    seg[i] = max(build(2*i, l, mid, torri), build((2*i)+1, mid, r, torri));

    //return the value of the segment
    return seg[i];
}

//recursive update of the segtree
void update(int i, int l, int r, int pos, long long int val) {

    if(r-l==1) { seg[i] = val; return; } //base case

    int mid = (l+r)/2; //find the middle
    if(pos<mid) update(2*i, l, mid, pos, val); //left half
    else update(2*i+1, mid, r, pos, val); //right half

    seg[i] = max(seg[2*i],seg[2*i+1]); //update with the max
}

int query_destra (int i, int l, int r, int ql, int qr, int x) {

    //base case
    if (ql >= r or qr <= l) return -1;//no intersection

    if (l >= ql and r <= qr) { //included
        if(seg[i] <= x) return -1; //if ... the node is not interesting

        //return i; <----------- IM MISSING SOMETHING HERE TO MAKE IT RETURN I CORRECTLY
    }

    int mid = (l+r)/2; //find the center

    //prioritizes the first value, if its not interesting, go to the second
    int ans = query_destra(2*i, l, mid, ql, qr, x);
    if(ans != -1) return ans;
    return query_destra(2*i+1, mid, r, ql, qr, x);
}

pair<int, int> chiedi(int x) {
    return make_pair(0 /*query_sinistra(1,0,sizeN, 0, x, torre[x])*/,query_destra(1, 0, sizeN, x, sizeN, torre[x]));
}

void cambia(int x, int h) {
    update(1, 0, sizeN, x, h);
}

void inizializza(int N, vector<int> H) {
    sizeN = H.size();
    torre.resize(sizeN);
    seg.resize(sizeN*4);
    for(int i=0; i<sizeN; i++) torre[i] = H[i];
    build(1,0,N,H);
}

I’ve been able to retrieve the highest in the range, but not the first, so i tried a different approach: I tried simply putting “return i” inside the included cases but from the results it gave me it was VERY wrong, and not putting somewhere “return i” simply makes it return -1 each time.

After failing on my own, i tried following what other people did, but not only i wasn’t able to understand most of the code they used, but it also didn’t work for what I needed to do.

An example of how the result should be, with a starting array of [6, 4, 2, 0, 8, 4], with x = 4 and my range going from position 1 to position 5, my program should be able to return 4 (the position of the 8, the first number higher than the starting one).
I have to do this thing for a number in the array both forwards and backwards.
Any help is appreciated, thanks in advance.