This is my rough idea:

1. Cat three strings together (e.g. abc$bc%cbc) and compute its SA and LCP:
2. Traverse through the SA. Assume the current string is C. For each of the three strings S and each (necessary) length L, maintain the number of suffix T of S that is already seen such that C[1...L]==T[1...L].

This is my actual code: 7273217. The numbers I maintained is put in stack<T> st;. I (unnecessarily) used binary index tree for range-modification.