REMMAX problem in may lunchtime 2019 - doesn't pass any testcases

https://www.codechef.com/problems/REMMAX
This is my solution to the problem. I can’t seem to find the corner cases for this sum.

My submission: https://www.codechef.com/viewsolution/24410018

i checked my solution for 1 till 10000 (using python code)
I used diff to see the difference and i could not find any differences in the output of these two codes (cpp code is the final code which i submitted):

python code for testing:

for n in xrange(1,10000+1):
	res = 1
	for i in xrange(1,n+1):
		number = i
		res = max(res,int(str(number)[::-1]))
	print res

cpp code:

#include <bits/stdc++.h>
using namespace std;

bool all9(string &str,int k){
	int flag = 0;
	for(int i=k;i<str.size();++i){
		if(str[i] != '9')
			return false;
	}
	return true;
}


int main(){
	int t;
	cin >> t;
	while(t--){
		string str;
		cin >> str;
		if(str.size()==1){
			cout << str << endl;
			continue;
		}

		int flag9 = 0, flag0 = 0;
		for(int i=0;i<str.size();++i) 
			if(str[i] == '9')
				flag9++;
			else if(str[i] == '0')
				flag0++;

		if(flag9 == str.size()){
			cout << str << endl;
			continue;
		}

		if(str[0]=='1' && flag0 == str.size()-1){
			cout << std::string(str.size()-1,'9') << endl;
			continue;
		}

		if(all9(str,1)){
			reverse(str.begin(),str.end());
			cout << str << endl;
			continue;
		}

		if((str[0]-'0')>1){
			str[0] = ((str[0]-'0')-1) + '0';
			for(int i=1;i<str.size();++i) str[i] = '9';
			reverse(str.begin(),str.end());
			cout << str << endl;
			continue;
		}
		else{
			int flag = 0;
			for(int i=1;i<str.size()-1;++i){
				if((str[i]-'0')>1 && !all9(str,i+1)){
					str[i] = ((str[i]-'0')-1) + '0';
					for(int j=i+1;j<str.size();++j) str[j] = '9';
					reverse(str.begin(),str.end());
					cout << str << endl;
					flag = 1;
					break;		
				}
				else if((str[i]-'0')==1 && !all9(str,i+1)){
					str[i] = '0';
					for(int j=i+1;j<str.size();++j) str[j] = '9';
					reverse(str.begin(),str.end());
					cout << str << endl;
					flag = 1;
					break;		
				}
			}
			if(flag == 0){
				reverse(str.begin(),str.end());
				cout << str << endl;	
			}
		}
	}
	return 0;
}

made a mistake. the output expected is how much the person should insert into the machine and not what the person will get from the machine. I was printing the later part.

thank you