Problem p03165 (python)

Fixed submission:
s = input()
t = input()

lens = len(s)
lent = len(t)

# dp = [[None] * lent for _ in range(lens)]
# def dfs(aindex=0, bindex=0):
#     if aindex >= lens:
#         return 0
#     if bindex >= lent:
#         return 0
#
#     if dp[aindex][bindex] is not None:
#         return dp[aindex][bindex]
#
#     if s[aindex] == t[bindex]:
#         r = dfs(aindex + 1, bindex + 1) + 1
#     else:
#         r = max(dfs(aindex + 1, bindex), dfs(aindex, bindex + 1))
#     dp[aindex][bindex] = r
#     return r
#
# print(dfs())

shift = [1 << x for x in range(3000 + 1)]

dp = [[0] * (lent + 1) for _ in range(lens + 1)]
for aindex in range(lens - 1, -1, -1):
    for bindex in range(lent - 1, -1, -1):
        if s[aindex] == t[bindex]:
            r = dp[aindex + 1][bindex + 1] + 1
        else:
            r = max(dp[aindex + 1][bindex], dp[aindex][bindex + 1])
        dp[aindex][bindex] = r

ans = ""
ls = len(s)
lt = len(t)
ls = 0
lt = 0
while ls < lens and lt < lent:
    if dp[ls][lt] == dp[ls + 1][lt]:
        ls += 1
    elif dp[ls][lt] == dp[ls][lt + 1]:
        lt += 1
    else:
        ans += t[lt]
        ls += 1
        lt += 1
print(ans)

Buggy submission (verdict: Runtime Error):
A = input()
B = input()

dp = [[None] * (len(B) + 1) for _ in range(len(A) + 1)]
def dfs(a=0, b=0):
    if a >= len(A) or b >= len(B):
        return 0

    if dp[a][b] is not None:
        return dp[a][b]

    match = A[a] == B[b]
    if match:
        r = dfs(a + 1, b + 1) + 1
    else:
        r = max(dfs(a + 1, b), dfs(a, b + 1))
    dp[a][b] = r
    return r

dfs()
# print(dfs())
# print(dp)

# print("---")
# for v in dp:
#     print(*map(lambda x: x if x is not None else "*", v))

def or_inf(v):
    return float('inf') if v is None else v

def reconst(a=0, b=0):
    if a >= len(A) or b >= len(B):
        return ''

    match = A[a] == B[b]
    if match:
        return reconst(a + 1, b + 1) + A[a]
    else:
        if or_inf(dp[a + 1][b]) >= or_inf(dp[a][b + 1]):
            return reconst(a + 1, b)
        else:
            return reconst(a, b + 1)
print(reconst()[::-1])

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

lens = len(s)
lent = len(t)

# dp = [[None] * lent for _ in range(lens)]
# def dfs(aindex=0, bindex=0):
#     if aindex >= lens:
#         return 0
#     if bindex >= lent:
#         return 0
#
#     if dp[aindex][bindex] is not None:
#         return dp[aindex][bindex]
#
#     if s[aindex] == t[bindex]:
#         r = dfs(aindex + 1, bindex + 1) + 1
#     else:
#         r = max(dfs(aindex + 1, bindex), dfs(aindex, bindex + 1))
#     dp[aindex][bindex] = r
#     return r
#
# print(dfs())

dp = [[0] * (lent + 1) for _ in range(lens + 1)]
pattern = [[0] * (lent + 1) for _ in range(lens + 1)]
# dp = [[(0, 0) for _ in range(lent + 1)] for _ in range(lens + 1)]
for aindex in range(lens - 1, -1, -1):
    for bindex in range(lent - 1, -1, -1):
        if s[aindex] == t[bindex]:
            r = dp[aindex + 1][bindex + 1] + 1
            # p = s[aindex] + pattern[aindex + 1][bindex + 1]
            # p = (1 << aindex) + pattern[aindex + 1][bindex + 1]
        else:
            if dp[aindex + 1][bindex] > dp[aindex][bindex + 1]:
                r = dp[aindex + 1][bindex]
                p = pattern[aindex + 1][bindex]
            else:
                r = dp[aindex][bindex + 1]
                p = pattern[aindex][bindex + 1]
            # r = max(dp[aindex + 1][bindex], dp[aindex][bindex + 1])
        dp[aindex][bindex] = r
        pattern[aindex][bindex] = p
for aindex in range(lens):
    if (1 << aindex) & pattern[0][0]:
        print(s[aindex], end="")
# print()
# print(dp[0])
# print(pattern[0])