# HTMLTAGS - Editorial

Setter: Bharat Singla
Tester: Felipe Mota
Editorialist: Aman Dwivedi

Cakewalk

None

# PROBLEM:

You are given a string S. Your task is to find whether the given string S is a valid closing HTML tag or not.

A closing HTML tag must:

• End with ">"
• Have only, and at least 1, lower-case alpha-numeric characters as its body

Help Chef by printing Success if the tag is fine. If not, print Error.

# QUICK EXPLANATION:

We have a string S, and our goal is to find whether the given string is a valid HTML tag or not. Let us check the condition one by one:

• It means that the first character of the given string should be < while the second character of this string should be /.

• If the starting two characters of string S fulfill the requirement, we will move to check another condition otherwise the string is not valid.

Case 2: It should end with ">"

• It means that the last character of the given string should be >.

• If the requirement is fulfilled we move to check the last condition left otherwise the string is not valid.

Case 3: Have only, and at least 1, lower-case alphanumeric characters as its body

• It means the remaining characters of the string S should contain only lowercase English alphabets ora digit and there should be at least one such character in the body.

• We can simply iterate on the remaining string and can check this condition.

If all the conditions are full-filled then the string S is considered to be valid otherwise not.

# TIME COMPLEXITY:

O(|S|) per test case

# SOLUTIONS:

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

void solve() {

string s;
cin >> s;
int n = s.length();

if (n < 4 or s.substr(0, 2) != "</" or s[n-1] != '>') {
cout << "Error\n";
return;
}

bool is_valid = true;
for (int i = 2; i < n - 1; i++) {
bool is_alpha = (s[i] >= 'a' and s[i] <= 'z');
bool is_num = (s[i] >= '0' and s[i] <= '9');
if (!is_alpha and !is_num) {
is_valid = false;
break;
}
}

cout << (is_valid ? "Success" : "Error") << endl;
}

int main() {

int tc;
cin >> tc;
while (tc--) solve();

return 0;
}
``````
Tester
``````#include <bits/stdc++.h>
using namespace std;
template<typename T = int> vector<T> create(size_t n){ return vector<T>(n); }
template<typename T, typename... Args> auto create(size_t n, Args... args){ return vector<decltype(create<T>(args...))>(n, create<T>(args...)); }
long long readInt(long long l,long long r,char endd){
long long x=0;
int cnt=0;
int fi=-1;
bool is_neg=false;
while(true){
char g=getchar();
if(g=='-'){
assert(fi==-1);
is_neg=true;
continue;
}
if('0'<=g && g<='9'){
x*=10;
x+=g-'0';
if(cnt==0){
fi=g-'0';
}
cnt++;
assert(fi!=0 || cnt==1);
assert(fi!=0 || is_neg==false);

assert(!(cnt>19 || ( cnt==19 && fi>1) ));
} else if(g==endd){
if(is_neg){
x= -x;
}
assert(l<=x && x<=r);
return x;
} else {
assert(false);
}
}
}
string ret="";
int cnt=0;
while(true){
char g=getchar();
assert(g!=-1);
if(g==endd){
break;
}
cnt++;
ret+=g;
}
assert(l<=cnt && cnt<=r);
return ret;
}
long long readIntSp(long long l,long long r){
}
long long readIntLn(long long l,long long r){
}
}
}
int main(){
ios::sync_with_stdio(false);
cin.tie(0);
while(t--){
for(auto c : s){
assert(33 <= c && c <= 126);
}
if(s.size() > 3){
bool ok = s[0] == '<' && s[1] == '/' && s[s.size() - 1] == '>';
for(int i = 2; i + 1 < s.size(); i++)
if(islower(s[i]) || isdigit(s[i]));
else ok = false;
cout << (ok ? "Success\n" : "Error\n");
} else {
cout << "Error\n";
}
}
return 0;
}

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

#define int long long

void solve()
{
bool ok = true;

string s;
cin>>s;

int n=(int)s.size();

if(n<4)
{
cout<<"Error"<<"\n";
return;
}

if(s[0]!='<' || s[1]!='/' || s[n-1]!='>')
ok=false;

if(ok)
{
for(int i=2;i<n-1;i++)
{
if(!((s[i]>='a' && s[i]<='z') ||
(s[i]>='0' && s[i]<='9')))
{
ok=false;
break;
}
}
}

if(ok)
cout<<"Success"<<"\n";
else
cout<<"Error"<<"\n";
}

int32_t main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);

int t;
cin>>t;

while(t--)
solve();

return 0;
}
``````

Can anyone explain me what is the error in this code?

``````#include <bits/stdc++.h>
#define ll long long
#define MOD 1e9 + 7
using namespace std;
// Use Ctrl+B to run

int main()
{
ios::sync_with_stdio(0);
cin.tie(0);
// freopen("input.txt", "r", stdin);
// freopen("output.txt", "w", stdout);
int t = 1;
cin >> t;
while (t--)
{
string s;
cin>>s;
if((s[0]=='<' && s[s.length()-1]=='>') && (s[1]=='/'))
{
bool ans = false;
for(int i=2; i<s.length()-1; i++)
{
if((((int)s[i])>=48 && ((int)s[i])<=57) || ((int)s[i])>=97 && ((int)s[i])<=122)
{
ans = true;
}
else
{
ans = false;
break;
}
}
if(ans)
{
cout<<"Success\n";
}
else
{
cout<<"Error\n";
}
}
else
{
cout<<"Error\n";
}
}

return 0;
}
``````

there is no error in your code it’s working fine

bro i did the same code but did not get submit

But it gave me WA
https://www.codechef.com/viewsolution/48214857
Oops got my mistake I am so frustrated now…

#include<bits/stdc++.h>
using namespace std;
int main(){
int t;
cin >> t;
while(t–){
string tag;
cin >> tag;
int cnt = 0, wrong = 0, space = 0;
for(int i = 2; i < tag.length() - 1; i++){
if((tag[i] >= 97 && tag[i] <= 122) || (tag[i] >= 48 && tag[i] <= 57)) cnt++;
else if(tag[i] == 32) space++;
else wrong++;
}
if((tag.length() - 3 - space == cnt ) && tag[0] == ‘<’ && tag[1] == ‘/’ && tag[tag.length() - 1] == ‘>’ && space >= 0){
cout << “Success\n”;
}
else cout << “Error\n”;
}
return 0;
}
// Can anyone help me out?

Fun to note that you can solve it in a few lines with a simple regex.

C++ solution

4 Likes

try giving input with lots of spaces. It would print ‘Error’ instead of ‘Success’

First error is that say I have a test case like this
</ > There is a space in between in that case it’ll fail. Another condition is say </> this is the case where there is nothing in it at that one also if fails.
Also group the statements
(!((s[I]>=97 && s[I]<=122) || (s[I]>=48 && s[I]<=57)))

You will have to see that its not an empty tag as well.For eg </>. This should print ‘Error’ as well.

Why getting wa ??
ll t ;
cin >> t;

``````while (t--) {
string tag;
cin >> tag;

int s = tag.size();
int op = tag.find_last_of("<");
int sl = tag.find_last_of("/");
int en = tag.find_last_of(">");
bool ch = false ;
nloop(i, s) {
if (isupper(tag[i])) {
cout << "Error" << nline;
ch = true;
break;
}
}
if (ch == true ) continue;
if (tag[0] == '<' && tag[1] == '/' && tag[s - 1] == '>' && op == 0 && sl == 1 && en == s - 1 && s >= 4  )
cout << "Success" << nline;
else
cout << "Error" << nline;
}``````

https://www.codechef.com/viewsolution/48200364

Consider the test input:

``````1
</4>
``````

Edit:

I’ll make a guess - consider the test input:

``````1
</>>
``````

this gives error for me:-
int n=s.size();
but when i declared n as long long it got submitted. Why n is long long? Constraint says that length(tag) is <=1000.
Can anyone explain this?

Please link to both solutions (the WA one and the AC one).

``````int main() {
fio;
ll t;
cin>>t;

while(t--){
string s;
cin>>s;

if(s[0]=='<' and s[1]=='/' and s[s.size() - 1]=='>' and s.size()>3){
bool check1=1;
for(ll i=2;i<s.size()-1;i++){
if(!(s[i]>='a' and s[i]<='z'|| s[i]>='1' and s[i]<='9')){

check1=0;
break;
}

}
if(check1){
cout<<"Success" nl;
}
else{
cout<<"Error" nl;
}
}
else{
cout<<"Error" nl;
}

}
``````

}

Can some tell me what is wrong in this…i am getting WA.

Can anyone please explain what the error is in my code?

``````for _ in range(int(input())):
tag_input = input()
tag = list(tag_input)
length = len(tag)
s = True
if length > 3 and tag[0: 2] == ['<', '/'] and tag[-1] == '>':
for i in range(3, length - 1):
if '1' <= tag[i] <= '9' or 'a' <= tag[i] <= 'z':
continue
else:
s = False
break
else:
s = False
if s:
print('Success')
else:
print('Error')
``````