Problem: 2050D - Digital string maximization
Language: C++17 (GCC 7-32)

Previous submission (verdict: Runtime error on test 3):
#include "bits/stdc++.h"
#include <iostream>
#include <complex>
#include <queue>
#include <set>
#include <unordered_set>
#include <list>
#include <chrono>
#include <random>
#include <iostream>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <map>
#include <unordered_map>
#include <stack>
#include <iomanip>
#include <fstream>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int,int> p32;
typedef pair<ll,ll> p64;
typedef pair<double,double> pdd;
typedef vector<ll> v64;
typedef vector<int> v32;
typedef vector<vector<int> > vv32;
typedef vector<vector<ll> > vv64;
typedef vector<vector<p64> > vvp64;
typedef vector<p64> vp64;
typedef vector<p32> vp32;
ll MOD = 998244353;
double eps = 1e-12;
#define forn(i,e) for(ll i = 0; i < e; i++)
#define forsn(i,s,e) for(ll i = s; i < e; i++)
#define rforn(i,s) for(ll i = s; i >= 0; i--)
#define rforsn(i,s,e) for(ll i = s; i >= e; i--)
#define ln "\n"
#define dbg(x) cout<<#x<<" = "<<x<<ln
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define INF 2e18
#define fast_cin() ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL)
#define all(x) (x).begin(), (x).end()
#define sz(x) ((ll)(x).size())


void solve(){
    long long n;
    cin>>n;
    string st = to_string(n);
    while(true){
        int biggestDiff = INT_MIN;
        int ind = 0;
        if(st.size()==1){
            cout<<n<<endl;
            return;
        }
        for(int i = 1; i<st.size();i++){
            if(st[i] == '0'){
                continue;
            }
            if (isdigit(st[i]) && isdigit(st[i - 1])) {
                int diff = stoll(string(1, st[i])) - stoll(string(1, st[i - 1]));
                if(diff == 1){
                    continue;
                }
                if (biggestDiff < diff && stoll(string(1, st[i])) > stoll(string(1, st[i - 1])) && diff>0) {
                    biggestDiff = diff;
                    ind = i;
                }
            }
        }
        if(biggestDiff == INT_MIN){
            break;
        }
        int store = stoll(st);
        swap(st[ind-1],st[ind]);
        st[ind-1]--;
        if(store>stoll(st)){
            st = to_string(store);
            break;
        }
    }
    cout<<st<<endl;
    return;
}
int main()
{
     fast_cin();
     ll t;
     cin >> t;
     for(int it=1;it<=t;it++) {
     //cout << "Case #" << it+1 << ": ";
        solve();
    }
    return 0;
}


Submission (verdict: Runtime error on test 3):
#include "bits/stdc++.h"
using namespace std;

typedef long long ll;
#define fast_cin() ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL)

void solve() {
    long long n;
    cin >> n;
    string st = to_string(n);

    while (true) {
        int biggestDiff = INT_MIN;
        int ind = 0;

        if (st.size() == 1) {
            cout << n << endl;
            return;
        }

        for (int i = 1; i < st.size(); i++) {
            if (st[i] == '0') {
                continue;
            }
            if (isdigit(st[i]) && isdigit(st[i - 1])) {
                int diff = stoi(string(1, st[i])) - stoi(string(1, st[i - 1]));
                if (diff == 1) {
                    continue;
                }
                if (biggestDiff < diff && stoi(string(1, st[i])) > stoi(string(1, st[i - 1])) && diff > 0) {
                    biggestDiff = diff;
                    ind = i;
                }
            }
        }

        if (biggestDiff == INT_MIN) {
            break;
        }

        int store = stoll(st);
        swap(st[ind - 1], st[ind]);
        st[ind - 1]--;
        
        if (store > stoll(st)) {
            st = to_string(store);
            break;
        }
    }

    cout << st << endl;
    return;
}

int main() {
    fast_cin();
    ll t;
    cin >> t;
    for (int it = 1; it <= t; it++) {
        solve();
    }
    return 0;
}