first_occurrences of length 26 with default values of -1, to store the first occurrence index of each character.c in the string s using its index i.c to its corresponding index in the alphabet (0 for 'a', 1 for 'b', etc.) by subtracting 'a' from it.first_occurrences at the character's index is -1, store i as the first occurrence.i and the stored first occurrence, and compare it to the expected distance from the distance array.false.true after the loop.