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

Previous 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() {
    string st;
    cin>>st;

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

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


Submission (verdict: Wrong answer on test 1):
#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() {
    string st;
    cin >> st;  

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

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

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

        if (biggestDiff == INT_MIN) {
            break;
        }

        string store = st; 
        swap(st[ind - 1], st[ind]); 
        st[ind - 1]--;  

        for (int i = 0; i < st.size(); i++) {
            if (st[i] < store[i]) {
                cout << store << endl;
                return;
            }
        }
    }
    cout << st << endl;
    return;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int t;
    cin >> t;  // Number of test cases
    while (t--) {
        solve();
    }

    return 0;
}