Question

Given two strings A and B of lowercase letters, return true if and only if we can swap two letters in A so that the result equals B.

Example 1:

Input: A = "ab", B = "ba" Output: true

Example 2:

Input: A = "ab", B = "ab" Output: false

Example 3:

Input: A = "aa", B = "aa" Output: true

Example 4:

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

Example 5:

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

Note:

1. 0 <= A.length <= 20000
2. 0 <= B.length <= 20000
3. A and B consist only of lowercase letters.

Solution

class Solution {
 public:
  bool buddyStrings(string A, string B) {
    int diff_num = 0;
    if (A.size() != B.size()) return false;
    for (int i = 0; i < A.size(); ++i) {
      if (A[i] != B[i]) diff_num++;
      if (diff_num > 2) return false;
    }

    if (diff_num == 1)
      return false;

    else if (diff_num == 2) {
      sort(A.begin(), A.end());
      sort(B.begin(), B.end());
      if (A == B) return true;
    }

    else {
      if (A.size() > 256) return true;
      bool result[256] = {false};
      for (size_t i = 0; i < A.size(); ++i) {
        if (result[A[i]])
          return true;
        else
          result[A[i]] = true;
      }
    }
    return false;
  }
};