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Variation of Atcoder Beginner Contest Problem — Make it Palindrome
https://atcoder.jp/contests/abc290/tasks/abc290_e
We have a variation of this, find sum of $$$F(x)$$$ for every subsequence of a string, and should be better than $$$O(N^2)$$$.
I can only think of $$$O(N^2)$$$ approach which involves finding individual contribution of every unequal pair of characters, can we optimize this?
