MATL, score 4

&=Rz

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###Explanation

Consider input 'ABBA' as an example.

&=   % Implicit input. Matrix of all equality comparisons
     % STACK: [1 0 0 1;
               0 1 1 0;
               0 1 1 0;
               1 0 0 1]
R    % Upper triangular part
     % STACK: [1 0 0 1;
               0 1 1 0;
               0 0 1 0;
               0 0 0 1]
z    % Number of nonzeros. Implicitly display
     % STACK: 6

MATL, score 4

&=Rz

Try it online!

Explanation

Consider input 'ABBA' as an example.

&=   % Implicit input. Matrix of all equality comparisons
     % STACK: [1 0 0 1;
               0 1 1 0;
               0 1 1 0;
               1 0 0 1]
R    % Upper triangular part
     % STACK: [1 0 0 1;
               0 1 1 0;
               0 0 1 0;
               0 0 0 1]
z    % Number of nonzeros. Implicitly display
     % STACK: 6

MATL, score 4

&=Rz

Try it online!

MATL, score 4

&=Rz

Try it online!

###Explanation

Consider input 'ABBA' as an example.

&=   % Implicit input. Matrix of all equality comparisons
     % STACK: [1 0 0 1;
               0 1 1 0;
               0 1 1 0;
               1 0 0 1]
R    % Upper triangular part
     % STACK: [1 0 0 1;
               0 1 1 0;
               0 0 1 0;
               0 0 0 1]
z    % Number of nonzeros. Implicitly display
     % STACK: 6