Check if One String Swap Can Make Strings Equal

My algorithm just iterates through s1 and s2 and checks the number of times s1[i] != s2[i]:

• if the number is equal to 0, then we can return true as the strings are identical
• if the number is equal to 2, and the unequal characters were at index positions i and j, then we just check that s1[index[0]] == s2[index[1]] && s1[index[1]] == s2[index[0]]
• else, then we can always return false

code

class Solution {
public:
    bool areAlmostEqual(string s1, string s2) {
        int index[2];
        int counter = 0;
        for(int i = 0; i < s1.size(); ++i) {
            if (s1[i] != s2[i]) {
                if (counter == 2) {
                    return false;
                }
                index[counter] = i;
                ++counter;
            }
        }
        if (counter == 0) {
            return true;
        }
        else if (counter != 2) {
            return false;
        } else {
            if (s1[index[0]] == s2[index[1]] and s1[index[1]] == s2[index[0]]) {
                return true;
            } else {
                return false;
            }
        }
    }
};

complexity

• Time: O(n)
• Space: O(1)