You are given two strings s
and t
of equal length n
. You can perform the following operation on the string s
:
s
of length l
where 0 < l < n
and append it at the start of s
.s = 'abcd'
then in one operation you can remove the suffix 'cd'
and append it in front of s
making s = 'cdab'
.You are also given an integer k
. Return the number of ways in which s
can be transformed into t
in exactly k
operations.
Since the answer can be large, return it modulo 109 + 7
.
Example 1:
Input: s = "abcd", t = "cdab", k = 2 Output: 2 Explanation: First way: In first operation, choose suffix from index = 3, so resulting s = "dabc". In second operation, choose suffix from index = 3, so resulting s = "cdab". Second way: In first operation, choose suffix from index = 1, so resulting s = "bcda". In second operation, choose suffix from index = 1, so resulting s = "cdab".
Example 2:
Input: s = "ababab", t = "ababab", k = 1 Output: 2 Explanation: First way: Choose suffix from index = 2, so resulting s = "ababab". Second way: Choose suffix from index = 4, so resulting s = "ababab".
Constraints:
2 <= s.length <= 5 * 105
1 <= k <= 1015
s.length == t.length
s
and t
consist of only lowercase English alphabets.When you get asked this question in a real-life environment, it will often be ambiguous (especially at FAANG). Make sure to ask these questions in that case:
The brute force approach is like trying every single possible combination to transform one string into another. We explore all potential changes, step by step, until we find a way to match the target string.
Here's how the algorithm would work step-by-step:
def string_transformation_brute_force(source_string, target_string, max_changes):
shortest_transformation = float('inf')
def explore_transformations(current_string, changes_made):
nonlocal shortest_transformation
if current_string == target_string:
shortest_transformation = min(shortest_transformation, changes_made)
return
if changes_made >= max_changes or changes_made >= shortest_transformation:
return
# Explore insertion
for index in range(len(current_string) + 1):
for char_code in range(ord('a'), ord('z') + 1):
new_string = current_string[:index] + chr(char_code) + current_string[index:]
explore_transformations(new_string, changes_made + 1)
# Explore deletion
for index in range(len(current_string)):
new_string = current_string[:index] + current_string[index + 1:]
# Recursively explore further transformations after deletion
explore_transformations(new_string, changes_made + 1)
# Explore substitution
for index in range(len(current_string)):
for char_code in range(ord('a'), ord('z') + 1):
# Avoid if character already exists
if current_string[index] == chr(char_code):
continue
new_string = current_string[:index] + chr(char_code) + current_string[index + 1:]
# Explore making transformations recursively
explore_transformations(new_string, changes_made + 1)
explore_transformations(source_string, 0)
if shortest_transformation == float('inf'):
return -1
else:
return shortest_transformation
The best way to solve this problem is to figure out, for each word, whether it should start a new line or be added to the existing one. We make these decisions based on how many characters are left on a line and what the rules for spacing are.
Here's how the algorithm would work step-by-step:
def string_transformation(input_string, max_line_length):
words = input_string.split()
result = ''
current_line = ''
for i, word in enumerate(words):
# Determine if adding the word exceeds the line length.
if len(current_line) == 0:
if len(word) <= max_line_length:
current_line = word
else:
result += word + '
'
elif len(current_line) + len(word) + 1 <= max_line_length:
current_line += ' ' + word
else:
result += current_line + '
'
current_line = word
# Handle the last line, left justifying it.
if i == len(words) - 1:
result += current_line
return result
Case | How to Handle |
---|---|
Null or empty input string | Return an empty string or throw an IllegalArgumentException as appropriate for the specification. |
Input string with length 1 | Return the original string as no transformation is needed. |
Input string containing only one unique character | The transformation should still apply based on the rule set, and should handle this case without errors. |
Input string with maximum allowed length | Verify that the solution's time and space complexity does not cause performance issues or memory errors with large inputs. |
Input string contains special characters or non-alphanumeric characters | Define how these characters should be handled: ignore, replace, or throw an error depending on the problem statement. |
Input string results in no possible transformation | Return the original string or an empty string, or indicate no transformation possible as required by the prompt. |
The transformed string is significantly longer than the initial string | Ensure memory allocation for the transformed string is sufficient to avoid buffer overflows or memory errors. |
Integer overflow during length calculation or character manipulation | Use appropriate data types (e.g., long) or error handling to prevent integer overflow. |