859. Buddy Strings

Given two strings `A` and `B` of lowercase letters, return `true` if you can swap two letters in `A` so the result is equal to `B`, 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 `A[i]` and `A[j]`. For example, swapping at indices `0` and `2` in `"abcd"` results in `"cbad"`.

Example 1:

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

Example 2:

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

Example 3:

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

Example 4:

```Input: A = "aaaaaaabc", B = "aaaaaaacb"
Output: true
```

Example 5:

```Input: A = "", B = "aa"
Output: false
```

Constraints:

• `0 <= A.length <= 20000`
• `0 <= B.length <= 20000`
• `A` and `B` consist of lowercase letters.

859. Buddy Strings
``````struct Solution;

use std::collections::HashSet;

impl Solution {
fn buddy_strings(a: String, b: String) -> bool {
let a: Vec<char> = a.chars().collect();
let b: Vec<char> = b.chars().collect();
let n = a.len();
let m = b.len();
if n != m {
return false;
}
if a == b {
let mut hs: HashSet<char> = HashSet::new();
let mut sum = 0;
for &c in &a {
if !hs.insert(c) {
sum += 1;
}
}
sum != 0
} else {
let mut pair: Vec<usize> = vec![];
for i in 0..n {
if a[i] != b[i] {
pair.push(i);
}
}
if pair.len() == 2 {
let i = pair[0];
let j = pair[1];
a[i] == b[j] && a[j] == b[i]
} else {
false
}
}
}
}

#[test]
fn test() {
let a = "ab".to_string();
let b = "ba".to_string();
assert_eq!(Solution::buddy_strings(a, b), true);
let a = "ab".to_string();
let b = "ab".to_string();
assert_eq!(Solution::buddy_strings(a, b), false);
let a = "aa".to_string();
let b = "aa".to_string();
assert_eq!(Solution::buddy_strings(a, b), true);
let a = "aaaaaaabc".to_string();
let b = "aaaaaaacb".to_string();
assert_eq!(Solution::buddy_strings(a, b), true);
let a = "".to_string();
let b = "aa".to_string();
assert_eq!(Solution::buddy_strings(a, b), false);
}
``````