# Buddy Strings Problem

## Description

LeetCode Problem 859.

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:

``````1
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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:

``````1
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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:

``````1
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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.
``````

Example 4:

``````1
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Input: s = "aaaaaaabc", goal = "aaaaaaacb"
Output: true
``````

Constraints:

• 1 <= s.length, goal.length <= 2 * 10^4
• s and goal consist of lowercase letters.

## Sample C++ Code

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class Solution {
public:
bool buddyStrings(string A, string B) {
if (A == B)
return (set<char>(A.begin(), A.end()).size() < A.size());

int n = A.length();
int l = 0, r = n-1;

while (l < n && A[l] == B[l])
l++;
while (r >= 0 && A[r] == B[r])
r--;
if (l < r)
swap(A[l], A[r]);

return A == B;
}
};
``````