Merge Sort (PROG - 0038: Toppykung)

#include <bits/stdc++.h>

using namespace std;

const int N = 1e3;
string str[N+10];
string L[N+10], R[N+10];

void merge(int l, int r){
    int mid = (l + r) / 2;
    int ll = mid - l + 1;
    int lr = r - mid;
    for(int i=1;i<=ll;i++) {
        if(!L[i].empty()) L[i].clear();
        L[i] += str[i+l-1];
    }
    for(int i=1;i<=lr;i++) {
        if(!R[i].empty()) R[i].clear();
        R[i] += str[mid+i];
    }
    int idx = l; // str[idx]
    int idl = 1;
    int idr = 1;
    while(idl <= ll and idr <= lr){
        str[idx].clear();
        if(L[idl] <= R[idr]){
            str[idx] += L[idl];
            idl ++;
        }
        else {
            str[idx] += R[idr];
            idr ++;
        }
        idx ++;
    }
    while(idl <= ll){
        str[idx].clear();
        str[idx] += L[idl];
        idl ++;
        idx ++;
    }
    while(idr <= lr){
        str[idx].clear();
        str[idx] += R[idr];
        idr ++;
        idx ++;
    }
}

void MergeSort(int l, int r){
    if(l == r) return;
    int mid = (l + r) / 2;
    MergeSort(l, mid);
    MergeSort(mid+1, r);
    merge(l, r);
}

int main(){

    int n;
    scanf("%d", &n);

    for(int i=1;i<=n;i++){
        cin >> str[i];
    }

    MergeSort(1, n);

    string prev;
    for(int i=1;i<=n;i++){
        if(str[i] != prev) cout << str[i] << "\n";
        if(prev.size() > 0) prev.clear();
        prev += str[i];
    }

    return 0;
}