Example 1:
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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:
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Input: A = "aaaaaaabc", B = "aaaaaaacb"
Output: true
Example 5:
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Input: A = "", B = "aa"
Output: false
​
​
Note:
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0 <= A.length <= 20000
0 <= B.length <= 20000
A and B consist only of lowercase letters.

class Solution {
public:
    bool buddyStrings(string A, string B) {
        if(A.length() != B.length() ) return false;
        if(A==B) 
        {
            vector<int>alpha(26,0);
            for(auto c:A)
            {
                if(++alpha[c-'a'] >1) return true;
            }
            return false;
        }
        int count=0;
        vector<int> index;
        for(int i=0;i<A.length();i++)
        {
            if(A[i] !=B[i]) 
            {
                count++;
                index.push_back(i);
            }
        }
        if(count !=2) return false;
        //cout<< index[0] <<" "<<index[1]<<endl;
        if(A[index[0]] == B[index[1]] && A[index[1]] == B[index[0]]) return true;
        return false;
    }
};