LeetCode 1239: Maximum Length of a Concatenated String with Unique Characters Solution
Master LeetCode problem 1239 (Maximum Length of a Concatenated String with Unique Characters), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.
1239. Maximum Length of a Concatenated String with Unique Characters
Problem Explanation
Explanation
To solve this problem, we can use backtracking to try all possible combinations of strings from the input array arr. At each step, we either include or exclude a string from the current combination. We need to make sure that the characters in the concatenated string are unique.
We will maintain a set to keep track of unique characters in the current combination. We will iterate through the strings in arr, and for each string, we will check if adding it to the current combination would result in duplicate characters. If not, we will include it in the combination and recursively explore further combinations.
The time complexity of this approach is exponential as we are trying all possible combinations. The space complexity is also exponential due to the recursive stack.
Solution Code
class Solution {
public int maxLength(List<String> arr) {
return backtrack(arr, 0, new HashSet<Character>(), 0);
}
private int backtrack(List<String> arr, int index, Set<Character> uniqueChars, int maxLength) {
if (index == arr.size()) {
return maxLength;
}
int withoutCurrString = backtrack(arr, index + 1, new HashSet<>(uniqueChars), maxLength);
String currString = arr.get(index);
Set<Character> currUniqueChars = new HashSet<>(uniqueChars);
boolean isValid = true;
for (char c : currString.toCharArray()) {
if (currUniqueChars.contains(c)) {
isValid = false;
break;
}
currUniqueChars.add(c);
}
int withCurrString = 0;
if (isValid) {
withCurrString = backtrack(arr, index + 1, currUniqueChars, maxLength + currString.length());
}
return Math.max(withoutCurrString, withCurrString);
}
}Try It Yourself
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