[859. Buddy Strings](https://leetcode.com/problems/buddy-strings/)

### 題目描述

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"`.

### 範例

**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 * 10^4^
* `s` and `goal` consist of lowercase letters.

### 解答

#### Javascript

function buddyStrings(s, goal) {
  if (s.length !== goal.length) return false;
  const different = [];
  for (let i = 0; i < s.length; i++) {
    if (s[i] !== goal[i]) {
      different.push(i);
    }
  }

  if (different.length === 2) {
    const [a, b] = different;
    if (s[a] === goal[b] && s[b] === goal[a]) return true;
  }

  // 全都一樣的情況
  if (different.length === 0) {
    const map = [];
    for (let i = 0; i < s.length; i++) {
      if (map[s[i]]) return true;
      map[s[i]] = true;
    }
  }

  return false;
}

> [name=Marsgoat] [time= Dec 2, 2022]

#### TypeScript

function buddyStrings(s: string, goal: string): boolean {
  if (s.length !== goal.length) return false;

  const hash = new Map<string, number>();
  s.split('').forEach((char) => hash.set(char, (hash.get(char) ?? 0) + 1));

  if (s === goal) {
    for (const value of hash.values()) {
      if (value !== 1) {
        return true;
      }
    }
    return false;
  }

  let swapCount = 0;
  goal.split('').forEach((char, i) => {
    if (char !== s[i]) {
      if (swapCount >= 2) return false;
      swapCount++;
    }
    const value = hash.get(char);
    if (value) {
      const newValue = value - 1;
      newValue ? hash.set(char, newValue) : hash.delete(char);
    }
  });

  return hash.size === 0;
}

> [name=Sheep] [time= July 3, 2023]

### Reference

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