How to get a substring by deleting minimum number of characters? - c++

Question

In this question, we take 2 strings as input say s1 and s2.
Now, first we need to check if s2 is a subsequence of s1. If not, print no.
But if it is, we need to print the minimum number of characters to be deleted from s1 to get s2.
Eg- thistext text
Here, text can be directly found without deleting any characters so the answer is 0.
Eg- cutefriendship crisp
In this case, the answer is 9.
What I've done so far,
#include <bits/stdc++.h>
using namespace std;
int checkIfSub(string s1, string s2, int m, int n)
{
int j = 0;
for(int i = 0; i < m && j < n; i++)
if(s1[i] == s2[j])
j++;
if(j == n)
return 0;
else
return 1;
}
int check(string s1, string s2)
{
int count = 0; string s3;
if(checkIfSub(s1, s2, s1.length(), s2.length()) == 1 || s2.length() > s1.length())
{
cout << "NO\n"; return 0;
}
int j = 0;
for(int i = 0; i < s1.length(); i++)
{
if(s1[i] == s2[j])
{
s3[j] = s1[j];
j++; continue;
}
count++;
}
cout << "YES " << count << "\n";
return 0;
}
int main() {
string s1, s2;
cin >> s1 >> s2;
check(s1, s2);
return 0;
}
My code works well for the second example, but fails the first case.
(This was a question asked in some interview I read online.)

Answer 1

Try something like this:
#include <iostream>
#include <string>
using namespace std;
bool check(const string &s1, const string &s2, int &minToDelete)
{
minToDelete = 0;
bool anySubSeqFound = false;
if (s2.empty())
return false;
string::size_type first = 0;
while ((first = s1.find(s2[0], first)) != string::npos)
{
int numDeleted = 0;
bool isSubSeq = true;
string::size_type next = first + 1;
for(string::size_type j = 1; j < s2.size(); ++j)
{
string::size_type found = s1.find(s2[j], next);
if (found == string::npos)
{
isSubSeq = false;
break;
}
numDeleted += (found - next);
next = found + 1;
}
if (isSubSeq)
{
if (anySubSeqFound)
{
if (numDeleted < minToDelete)
minToDelete = numDeleted;
}
else
{
anySubSeqFound = true;
minToDelete = numDeleted;
}
}
++first;
}
return anySubSeqFound;
}
int main()
{
int minToDelete;
if (check("thistext", "text", minToDelete))
cout << "yes, delete " << minToDelete << endl;
else
cout << "no" << endl;
if (check("cutefriendship", "crisp", minToDelete))
cout << "yes, delete " << minToDelete << endl;
else
cout << "no" << endl;
}
Live Demo