Given two strings A and B, the task is to count the minimum number of operations required to construct the string B by following operations:
- Select a subsequence of the string A.
- Append the subsequence at the newly formed string (initially empty).
Print the minimum count of operations required. If it is impossible to make the new string equal to B by applying the given operations, then print -1.
Input: A = “abc”, B = “abac”
Initially, C = “”.
Step 1: Select subsequence “ab” from string A and append it to the empty string C, i.e. C = “ab”.
Step 2: Select subsequence “ac” from string A and append it to the end of string C, i.e. C = “abac”.
Now, the string C is same as string B.
Therefore, count of operations required is 2.
Input: A = “geeksforgeeks”, B = “programming”
Approach: Follow the below steps to solve this problem:
- Initialize a Map to map characters present in the string A with their respective indices.
- For each character in string A, keep track of all of its occurrences.
- Initialize a variable, say ans, to store the count of operations required. As the number of operations must be greater than 1, set ans = 1.
- Iterate over the characters of string B and check if the character is present in the string A or not by using the Map.
- Lastly, maximize the length of the subsequence chosen from the string A for each operation.
- Finally, print the minimum operations required.
Below is the implementation of the above approach:
Time Complexity: O(N * logN)
Auxiliary Space: O(N)