LeetCode 859: Buddy Strings Solution

Master LeetCode problem 859 (Buddy Strings), a easy 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.

859. Buddy Strings

Easy

Hash Table String

Problem Explanation

Explanation

To solve this problem, we need to check if we can swap two characters in string s to make it equal to string goal. We can have two cases:

If s and goal are equal, we need to check if there are at least two characters that are the same in s. If so, we can swap these two characters to get the same string.
If s and goal are not equal, we need to check if there are exactly two pairs of characters that are different between s and goal. If so, we can swap these two pairs to make s equal to goal.

Algorithm

If the lengths of s and goal are not equal, return false.
If s is equal to goal, check if there are at least two characters that are the same in s by using a set.
If s is not equal to goal, iterate over both strings and store the indices of different characters in separate lists. Check if there are exactly two pairs of different characters.
Return true if any of the conditions are met, otherwise return false.

Time complexity: O(n) Space complexity: O(n)

Solution Code

class Solution {
    public boolean buddyStrings(String s, String goal) {
        if (s.length() != goal.length()) {
            return false;
        }
        
        if (s.equals(goal)) {
            Set<Character> set = new HashSet<>();
            for (char c : s.toCharArray()) {
                if (set.contains(c)) {
                    return true;
                }
                set.add(c);
            }
        } else {
            List<Integer> diffIndices = new ArrayList<>();
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) != goal.charAt(i)) {
                    diffIndices.add(i);
                }
            }
            if (diffIndices.size() != 2) {
                return false;
            }
            return s.charAt(diffIndices.get(0)) == goal.charAt(diffIndices.get(1)) && s.charAt(diffIndices.get(1)) == goal.charAt(diffIndices.get(0));
        }
        
        return false;
    }
}

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