Compute x⍳x where x is a vector of strings. Begin with an O(n*2) solution.

   xix←{(1+≢⍵)-+/∨\⍵∘.≡⍵}

   x← ⍕¨ ?1e3⍴1e5
   (xix x) ≡ x ⍳ x
1

   ⎕←t←{x∘←⍕¨?⍵⍴1e5 ⋄ 1 1 cmpx 'xix x'}¨ 1e3×1 2 4 8 16
0.000319824 0.000944824 0.00304688 0.0108516 0.0429062

   2 ÷⍨/ t
2.9542 3.22481 3.56154 3.95392