Question

859. Buddy Strings

中文文档

Description

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.

Solutions

Solution 1

class Solution:
  def buddyStrings(self, s: str, goal: str) -> bool:
    m, n = len(s), len(goal)
    if m != n:
      return False
    cnt1, cnt2 = Counter(s), Counter(goal)
    if cnt1 != cnt2:
      return False
    diff = sum(s[i] != goal[i] for i in range(n))
    return diff == 2 or (diff == 0 and any(v > 1 for v in cnt1.values()))

class Solution {
  public boolean buddyStrings(String s, String goal) {
    int m = s.length(), n = goal.length();
    if (m != n) {
      return false;
    }
    int diff = 0;
    int[] cnt1 = new int[26];
    int[] cnt2 = new int[26];
    for (int i = 0; i < n; ++i) {
      int a = s.charAt(i), b = goal.charAt(i);
      ++cnt1[a - 'a'];
      ++cnt2[b - 'a'];
      if (a != b) {
        ++diff;
      }
    }
    boolean f = false;
    for (int i = 0; i < 26; ++i) {
      if (cnt1[i] != cnt2[i]) {
        return false;
      }
      if (cnt1[i] > 1) {
        f = true;
      }
    }
    return diff == 2 || (diff == 0 && f);
  }
}

class Solution {
public:
  bool buddyStrings(string s, string goal) {
    int m = s.size(), n = goal.size();
    if (m != n) return false;
    int diff = 0;
    vector<int> cnt1(26);
    vector<int> cnt2(26);
    for (int i = 0; i < n; ++i) {
      ++cnt1[s[i] - 'a'];
      ++cnt2[goal[i] - 'a'];
      if (s[i] != goal[i]) ++diff;
    }
    bool f = false;
    for (int i = 0; i < 26; ++i) {
      if (cnt1[i] != cnt2[i]) return false;
      if (cnt1[i] > 1) f = true;
    }
    return diff == 2 || (diff == 0 && f);
  }
};

func buddyStrings(s string, goal string) bool {
  m, n := len(s), len(goal)
  if m != n {
    return false
  }
  diff := 0
  cnt1 := make([]int, 26)
  cnt2 := make([]int, 26)
  for i := 0; i < n; i++ {
    cnt1[s[i]-'a']++
    cnt2[goal[i]-'a']++
    if s[i] != goal[i] {
      diff++
    }
  }
  f := false
  for i := 0; i < 26; i++ {
    if cnt1[i] != cnt2[i] {
      return false
    }
    if cnt1[i] > 1 {
      f = true
    }
  }
  return diff == 2 || (diff == 0 && f)
}

function buddyStrings(s: string, goal: string): boolean {
  const m = s.length;
  const n = goal.length;
  if (m != n) {
    return false;
  }
  const cnt1 = new Array(26).fill(0);
  const cnt2 = new Array(26).fill(0);
  let diff = 0;
  for (let i = 0; i < n; ++i) {
    cnt1[s.charCodeAt(i) - 'a'.charCodeAt(0)]++;
    cnt2[goal.charCodeAt(i) - 'a'.charCodeAt(0)]++;
    if (s[i] != goal[i]) {
      ++diff;
    }
  }
  for (let i = 0; i < 26; ++i) {
    if (cnt1[i] != cnt2[i]) {
      return false;
    }
  }
  return diff == 2 || (diff == 0 && cnt1.some(v => v > 1));
}