Is Buddy Strings easy or hard?

Buddy Strings is classified as an Easy problem on LeetCode. The main challenge is handling edge cases, especially when the two strings are already identical and require a duplicate character to allow a valid swap.

How to solve Buddy Strings in O(n)?

Traverse both strings and store positions where characters differ. If more than two mismatches appear, the answer is false. When exactly two mismatches exist, check if swapping those two characters in the first string matches the second. Handle the edge case where both strings are identical by verifying that a duplicate character exists.

What is the best approach for Buddy Strings?

The direct comparison approach is the most common solution. Iterate through both strings and record indices where characters differ. If there are exactly two mismatches and swapping those characters makes the strings equal, return true. This runs in O(n) time with O(1) extra space.

What data structure is used in Buddy Strings?

Most solutions use simple string traversal with optional help from a hash table or frequency array. A set or counting array helps detect duplicate characters when the strings are already identical.

What is the time complexity of Buddy Strings?

The optimal solution runs in O(n) time where n is the string length. You perform a single pass to detect mismatches or compute character frequencies. Space complexity is O(1) because only a few variables or a fixed-size frequency array are required.

Buddy Strings Python or Java solution approach?

Python or Java implementations typically iterate through the strings to track mismatch indices. Some versions also use a frequency array to confirm both strings contain the same characters. Both approaches achieve O(n) time complexity.

Is Buddy Strings asked at Google, Amazon, or Meta?

Buddy Strings appears in coding interview practice sets similar to those used by companies like Amazon and Google. The problem tests string manipulation, edge case handling, and basic hash or counting techniques, which are common interview topics.

Description Solution Video 15:42

859. Buddy Strings

Easy34.0% acceptance5 companies

Given two strings s and goal, return true if you can swap two letters in s so the result is equal to goal, otherwise, return false.

Swapping letters is defined as taking two indices i and j (0-indexed) such that i != j and swapping the characters at s[i] and s[j].

For example, swapping at indices 0 and 2 in "abcd" results in "cbad".

Example 1:

Input: s = "ab", goal = "ba"
Output: true
Explanation: You can swap s[0] = 'a' and s[1] = 'b' to get "ba", which is equal to goal.

Example 2:

Input: s = "ab", goal = "ab"
Output: false
Explanation: The only letters you can swap are s[0] = 'a' and s[1] = 'b', which results in "ba" != goal.

Example 3:

Input: s = "aa", goal = "aa"
Output: true
Explanation: You can swap s[0] = 'a' and s[1] = 'a' to get "aa", which is equal to goal.

Constraints:

1 <= s.length, goal.length <= 2 * 10⁴
s and goal consist of lowercase letters.

Asked at 5 companies

DoorDash Zoho

Google Amazon Meta

Topics

Hash Table String

15:42

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859. Buddy Strings

Asked at 5 companies

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