class Group(NamedTuple):
    char: str
    count: int

def substrCount(n, s):
    total = 0
    groups = []
    group = Group(char=s[0], count=1)

    # iterate over 's', grouping runs of same char
    for char in s[1:]:
        if group.char == char:  # increment current char count
            group = Group(char=char, count=1 + group.count)
        else:  # register current group, restart count w/ new group
            groups.append(group)
            total += (group.count**2 + group.count) // 2  # n substrings
            group = Group(char=char, count=1)  # restart w/ new char

    # register final group
    groups.append(group)
    total += (group.count**2 + group.count) // 2  # n substrings in group

    # iterate over triplets of groups, counting
    # odd sized substrings w/ extra middle char
    for before, current, after in zip(groups, groups[1:], groups[2:]):
        if current.count == 1 and before.char == after.char:
            total += min(before.count, after.count)

    return total