字符串中PAT计数

def solve(s):
    p_count = 0
    pa_count = 0
    pat_count = 0
    for c in s:
        if c == 'P':
            p_count += 1
        elif c == 'A':
            pa_count += p_count
        elif c == 'T':
            pat_count += pa_count
    print(pat_count % 1000000007)