Ordered Segment Tree - YessineJallouli/Competitive-Programming GitHub Wiki

#include <bits/stdc++.h>
#define ll long long
#define SaveTime ios_base::sync_with_stdio(false), cin.tie(0);
using namespace std;

vector<int> mrg(vector<int> &a, vector<int> &b) {
    int i = 0, j = 0;
    vector<int> res;
    while (i < a.size() && j < b.size()) {
        if (a[i] < b[j]) {
            res.push_back(a[i++]);
        }
        else
            res.push_back(b[j++]);
    }
    while (i < a.size())
        res.push_back(a[i++]);
    while (j < b.size())
        res.push_back(b[j++]);
    return res;
}

const int N = 1e5+7;
vector<int> tree[4*N];
int a[N];
int n;

void build(int id = 0, int ns = 0, int ne = n-1) {
    if (ns == ne) {
        tree[id].push_back(a[ns]);
        return;
    }
    int md = (ns+ne)/2;
    int l = 2*id+1;
    int r = 2*id+2;
    build(l, ns, md);
    build(r, md+1, ne);
    tree[id] = mrg(tree[l], tree[r]);
}

int main() {
    SaveTime
    cin >> n;
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
    build();
}