1790. Check if One String Swap Can Make Strings Equal

Problem

You are given two strings s1 and s2 of equal length. A string swap is an operation where you choose two indices in a string (not necessarily different) and swap the characters at these indices.

Return true **if it is possible to make both strings equal by performing **at most one string swap **on *exactly one* of the strings. **Otherwise, return false.

  Example 1:

Input: s1 = "bank", s2 = "kanb"
Output: true
Explanation: For example, swap the first character with the last character of s2 to make "bank".

Example 2:

Input: s1 = "attack", s2 = "defend"
Output: false
Explanation: It is impossible to make them equal with one string swap.

Example 3:

Input: s1 = "kelb", s2 = "kelb"
Output: true
Explanation: The two strings are already equal, so no string swap operation is required.

  Constraints:

• 1 <= s1.length, s2.length <= 100

• s1.length == s2.length

• s1 and s2 consist of only lowercase English letters.

Solution (Java)

class Solution {
    public boolean areAlmostEqual(String s1, String s2) {
        int i1 = -1;
        int i2 = -1;
        // We go though the two strings
        for (int i = 0; i < s1.length(); i++) {
            // check if each char is the same.
            if (s1.charAt(i) == s2.charAt(i)) {
                continue;
            }
            // When there are more than 2 char different., we return false;
            if (i2 != -1) {
                return false;
            }
            // If there is char that is different, we record the index.
            if (i1 == -1) {
                i1 = i;
            } else {
                // If there is char that is different, we record the index.
                i2 = i;
            }
        }
        // When three is no different char, we return true;
        if (i1 == i2) {
            return true;
        }
        // When there is 1 char different, we return false;
        if (i2 == -1) {
            return false;
        }
        // When there are 2 char different, and swap them can make two string equal, we return true;
        return s1.charAt(i1) == s2.charAt(i2) && s1.charAt(i2) == s2.charAt(i1);
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).