Solve three algorithmic OA tasks

Task 1 (Odd-frequency string): Given an integer N in [1..200000], write an algorithm that returns any length-N string of lowercase letters (a–z) such that every letter that appears occurs an odd number of times. Task 2 (Min-difference with minimal swaps): Given two equal-length digit strings S and T (length N up to 100000, digits only, no leading zeros), you may choose a subset of indices and swap S[i] with T[i] at each chosen index. Among all swap choices that minimize |int(S) − int(T)|, return the minimum number of swaps required. For example, S = "29162" and T = "10524" should return 2. Task 3 (Two-choice slot assignment): Given arrays A and B of length N (1 ≤ A[k], B[k] ≤ S, A[k] ≠ B[k]) and an integer S (2.. 100000), determine whether it is possible to assign every patient k to either A[k] or B[k] so that at most one patient is assigned to each slot. Return true if such an assignment exists, otherwise false.