Buggy python submission (verdict: Time Limit Exceeded):
s = input()

dp = [[0 for _ in range(4)] for _ in range(len(s) + 1)]
dp[len(s)][3] = 1

for i in reversed(range((len(s)))):
    m = 1
    m1 = 1
    m2 = 0
    m3 = 0
    m4 = 0
    if s[i] == '?':
        m = 3
        m1 = 3
        m2 = 1
        m3 = 1
        m4 = 1

    if s[i] == 'C':
        m2 = 1

    if s[i] == 'B':
        m3 = 1

    if s[i] == 'A':
        m4 = 1

    dp[i][3] = m * dp[i+1][3]
    dp[i][2] = m1 * dp[i+1][2] + m2 * dp[i+1][3]
    dp[i][1] = m1 * dp[i+1][1] + m3 * dp[i+1][2]
    dp[i][0] = m1 * dp[i+1][0] + m4 * dp[i+1][1]

n = 10 ** 9 + 7
ans = dp[0][0] % n
print(ans)

Fixed submission:
s = input()

dp = [[0 for _ in range(4)] for _ in range(len(s) + 1)]
dp[len(s)][3] = 1
n = 10 ** 9 + 7

for i in reversed(range((len(s)))):
    m = 1
    m1 = 1
    m2 = 0
    m3 = 0
    m4 = 0
    if s[i] == '?':
        m = 3
        m1 = 3
        m2 = 1
        m3 = 1
        m4 = 1

    if s[i] == 'C':
        m2 = 1

    if s[i] == 'B':
        m3 = 1

    if s[i] == 'A':
        m4 = 1

    dp[i][3] = (m * dp[i+1][3]) % n
    dp[i][2] = (m1 * dp[i+1][2] + m2 * dp[i+1][3]) % n
    dp[i][1] = (m1 * dp[i+1][1] + m3 * dp[i+1][2]) % n
    dp[i][0] = (m1 * dp[i+1][0] + m4 * dp[i+1][1]) % n

ans = dp[0][0]
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
s = input()

dp3 = 1
dp2 = 0
dp1 = 0
dp0 = 0

for i in reversed(range((len(s)))):
    m = 1
    m1 = 1
    m2 = 0
    m3 = 0
    m4 = 0
    if s[i] == '?':
        m = 3
        m1 = 3
        m2 = 1
        m3 = 1
        m4 = 1

    if s[i] == 'C':
        m2 = 1

    if s[i] == 'B':
        m3 = 1

    if s[i] == 'A':
        m4 = 1

    t_dp3 = m * dp3
    t_dp2 = m1 * dp2 + m2 * dp3
    t_dp1 = m1 * dp1 + m3 * dp2
    t_dp0 = m1 * dp0 + m4 * dp1
    dp3 = t_dp3
    dp2 = t_dp2
    dp1 = t_dp1
    dp0 = t_dp0

n = 10 ** 9 + 7
ans = dp0 % n
print(ans)

Fixed submission:
s = input()

dp = [[0 for _ in range(4)] for _ in range(len(s) + 1)]
dp[len(s)][3] = 1
n = 10 ** 9 + 7

for i in reversed(range((len(s)))):
    m = 1
    m1 = 1
    m2 = 0
    m3 = 0
    m4 = 0
    if s[i] == '?':
        m = 3
        m1 = 3
        m2 = 1
        m3 = 1
        m4 = 1

    if s[i] == 'C':
        m2 = 1

    if s[i] == 'B':
        m3 = 1

    if s[i] == 'A':
        m4 = 1

    dp[i][3] = (m * dp[i+1][3]) % n
    dp[i][2] = (m1 * dp[i+1][2] + m2 * dp[i+1][3]) % n
    dp[i][1] = (m1 * dp[i+1][1] + m3 * dp[i+1][2]) % n
    dp[i][0] = (m1 * dp[i+1][0] + m4 * dp[i+1][1]) % n

ans = dp[0][0]
print(ans)

Buggy python submission (verdict: Runtime Error):
s = input()

dp3 = 1
dp2 = 0
dp1 = 0
dp0 = 0

for i in reversed(range((len(s)))):
    m = 1
    m1 = 1
    m2 = 0
    m3 = 0
    m4 = 0
    if s[i] == '?':
        m = 3
        m1 = 3
        m2 = 1
        m3 = 1
        m4 = 1

    if s[i] == 'C':
        m2 = 1

    if s[i] == 'B':
        m3 = 1

    if ss[i] == 'A':
        m4 = 1

    t_dp3 = m * dp3
    t_dp2 = m1 * dp2 + m2 * dp3
    t_dp1 = m1 * dp1 + m3 * dp2
    t_dp0 = m1 * dp0 + m4 * dp1
    dp3 = t_dp3
    dp2 = t_dp2
    dp1 = t_dp1
    dp0 = t_dp0

n = 10 ** 9 + 7
ans = dp0 % n
print(ans)

Fixed submission:
s = input()

dp = [[0 for _ in range(4)] for _ in range(len(s) + 1)]
dp[len(s)][3] = 1
n = 10 ** 9 + 7

for i in reversed(range((len(s)))):
    m = 1
    m1 = 1
    m2 = 0
    m3 = 0
    m4 = 0
    if s[i] == '?':
        m = 3
        m1 = 3
        m2 = 1
        m3 = 1
        m4 = 1

    if s[i] == 'C':
        m2 = 1

    if s[i] == 'B':
        m3 = 1

    if s[i] == 'A':
        m4 = 1

    dp[i][3] = (m * dp[i+1][3]) % n
    dp[i][2] = (m1 * dp[i+1][2] + m2 * dp[i+1][3]) % n
    dp[i][1] = (m1 * dp[i+1][1] + m3 * dp[i+1][2]) % n
    dp[i][0] = (m1 * dp[i+1][0] + m4 * dp[i+1][1]) % n

ans = dp[0][0]
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
s = input()

dp3 = 1
dp2 = 0
dp1 = 0
dp0 = 0

for i in reversed(range((len(s)))):
    if s[i] == '?':
        m = 3
    else:
        m = 1

    if s[i] == '?':
        m1 = 3
    else:
        m1 = 1

    if s[i] == '?' or s[i] == 'C':
        m2 = 1
    else:
        m2 = 0

    if s[i] == '?' or s[i] == 'B':
        m3 = 1
    else:
        m3 = 0

    if s[i] == '?' or s[i] == 'A':
        m4 = 1
    else:
        m4 = 0

    t_dp3 = m * dp3
    t_dp2 = m1 * dp2 + m2 * dp3
    t_dp1 = m1 * dp1 + m3 * dp2
    t_dp0 = m1 * dp0 + m4 * dp1
    dp3 = t_dp3
    dp2 = t_dp2
    dp1 = t_dp1
    dp0 = t_dp0

n = 10 ** 9 + 7
ans = dp0 % n
print(ans)

Fixed submission:
s = input()

dp = [[0 for _ in range(4)] for _ in range(len(s) + 1)]
dp[len(s)][3] = 1
n = 10 ** 9 + 7

for i in reversed(range((len(s)))):
    m = 1
    m1 = 1
    m2 = 0
    m3 = 0
    m4 = 0
    if s[i] == '?':
        m = 3
        m1 = 3
        m2 = 1
        m3 = 1
        m4 = 1

    if s[i] == 'C':
        m2 = 1

    if s[i] == 'B':
        m3 = 1

    if s[i] == 'A':
        m4 = 1

    dp[i][3] = (m * dp[i+1][3]) % n
    dp[i][2] = (m1 * dp[i+1][2] + m2 * dp[i+1][3]) % n
    dp[i][1] = (m1 * dp[i+1][1] + m3 * dp[i+1][2]) % n
    dp[i][0] = (m1 * dp[i+1][0] + m4 * dp[i+1][1]) % n

ans = dp[0][0]
print(ans)