Wrong answer in Abbreviations problem using DP - c++

Question

Can someone explain what is wrong with my code? I am getting "Abort called" in 7 test cases. Rest are successful.
I have a 2d dp array with of size: n+1 x m+1 were n and m are sizes of a and b respectively. So, the row represent string a and columns represent string b.
First, I set dp[0][0] to 1 since it is possible to turn empty string into empty.
So, initially, i am checking if I can turn any substring of a into the empty string (in the first single for-loop). This is true for all substrings of a without any capital letters. As soon as there is a capital letter, the rest of the substrings cannot be converted.
Then (in the next double for-loop), I am examining all the cases.
Case 1: a[i-1] == b[i-1] -> if both the letter are the exact same, then dp[i][j] = dp[i-1][j-1]
Case 2: a[i-1] is lower case (this has 2 sub cases):
Case 2.1: a[i-1] and b[j-1] are the same letter (but not the same case) -> then we can either change a[i-1] or delete it . So:
dp[i][j] = dp[i-1][j-1] || dp[i-1][j].
Case 2.2: a[i-1] and b[j-1] are not the same -> in this case, we can only delete a[i-1] since it is lower case . So: dp[i][j] =
dp[i-1][j]
Link to problem: https://www.hackerrank.com/challenges/abbr/problem?h_l=interview&playlist_slugs%5B%5D=interview-preparation-kit&playlist_slugs%5B%5D=dynamic-programming
P.S. The main logic of the program is just inside the abbreviation() function.
Code (EDITTED):
#include <bits/stdc++.h>
using namespace std;
bool isSame(const char &a, const char &b)
{
return a == b || abs(a - b) == 32;
}
bool isLower(const char &a)
{
return a > 90 && a < 123;
}
// Complete the abbreviation function below.
string abbreviation(const string &a, const string &b)
{
int n = a.size(), m = b.size();
if (m > n)
return "NO";
vector<vector<bool>> dp(n + 1, vector<bool>(m + 1, 0));
dp[0][0] = 1;
for (int i = 1; i <= n; ++i)
{
if (isLower(a[i - 1]) && dp[i - 1][0])
dp[i][0] = 1;
}
for (int i = 1; i <= n; ++i)
{
for (int j = 1; j <= i; ++j)
{
if (a[i - 1] == b[j - 1])
dp[i][j] = dp[i - 1][j - 1];
if (isLower(a[i - 1]))
{
if (isSame(a[i - 1], b[j - 1]))
dp[i][j] = dp[i - 1][j - 1] || dp[i - 1][j];
else if (dp[i - 1][j])
{
dp[i][j] = dp[i - 1][j];
}
}
}
}
return dp[n][m] ? "YES" : "NO";
}
int main()
{
int t;
cin >> t;
cin.ignore(numeric_limits<streamsize>::max(), '\n');
while (t--)
{
string a, b;
getline(cin, a);
getline(cin, b);
cout << abbreviation(a, b) << "\n";
}
return 0;
}

Answer 1

The error in the code is "Segmentation fault".
Because of the following loop:
for (int j = 1; j <= i; ++j)
As the loop is iterating till i(which could be greater than m i.e. the size of b). That's the reason for the Segmentation fault.
Now the following code passes all the test cases.
#include <bits/stdc++.h>
using namespace std;
bool isSame(const char&a, const char&b){
return a==b || abs(a-b)==32;
}
bool isLower(const char&a){
return a >90 && a<123;
}
// Complete the abbreviation function below.
string abbreviation(string a, string b) {
int n = a.size(), m = b.size();
if(m>n)
return "NO";
int dp[n+1][m+1] = {};
dp[0][0] = 1;
for(int i=1; i<=n; ++i)
if(isLower(a[i-1]) && dp[i-1][0])
dp[i][0] = 1;
for(int i=1; i<=n; ++i)
for(int j =1; j<=min(i,m); ++j){
if(a[i-1]==b[j-1])
dp[i][j] = dp[i-1][j-1];
if(isLower(a[i-1]))
{
if(isSame(a[i-1], b[j-1]))
dp[i][j] = dp[i-1][j-1] || dp[i-1][j];
else if(dp[i-1][j])
dp[i][j] = dp[i-1][j];
}
}
return dp[n][m] ? "YES" : "NO";
}
int main()
{
int q;
cin >> q;
cin.ignore(numeric_limits<streamsize>::max(), '\n');
for (int q_itr = 0; q_itr < q; q_itr++) {
string a;
getline(cin, a);
string b;
getline(cin, b);
string result = abbreviation(a, b);
cout << result << "\n";
}
return 0;
}