Buggy python submission (verdict: Time Limit Exceeded):
x = input()
y = input()
lx = len(x)
ly = len(y)

lcs = [[''] * (ly + 1) for _ in range(lx + 1)]
for i_x in range(lx):
    for i_y in range(ly):
        if x[i_x] == y[i_y]:
            lcs[i_x+1][i_y+1] = lcs[i_x][i_y] + x[i_x]
        else:
            lcs[i_x+1][i_y+1] = max(lcs[i_x+1][i_y], lcs[i_x][i_y+1], key=len)

print(lcs[-1][-1])


Fixed submission:
x = input()
y = input()
lx = len(x)
ly = len(y)

chars = [[''] * (ly + 1) for _ in range(lx + 1)]
length = [[0] * (ly + 1) for _ in range(lx + 1)]
prev = [[0b00] * (ly + 1) for _ in range(lx + 1)]

for i_x in range(lx):
    for i_y in range(ly):
        if x[i_x] == y[i_y]:
            length[i_x+1][i_y+1] = length[i_x][i_y] + 1
            chars[i_x+1][i_y+1] = x[i_x]
            prev[i_x+1][i_y+1] = 0b11
        elif length[i_x+1][i_y] > length[i_x][i_y+1]:
            length[i_x+1][i_y+1] = length[i_x+1][i_y]
            prev[i_x+1][i_y+1] = 0b01
        else:
            length[i_x+1][i_y+1] = length[i_x][i_y+1]
            prev[i_x+1][i_y+1] = 0b10

lcs = [''] * length[-1][-1]
i_x, i_y = lx, ly
i = 1
while i_x and i_y:
    if prev[i_x][i_y] == 0b11:
        lcs[-i] = chars[i_x][i_y]
        i += 1
    i_x, i_y = i_x - ((prev[i_x][i_y] & 0b10) >> 1), i_y - (prev[i_x][i_y] & 0b01)

print(''.join(lcs))

Buggy python submission (verdict: Time Limit Exceeded):
x = input()
y = input()
lx = len(x)
ly = len(y)

chars = [[''] * (ly + 1) for _ in range(lx + 1)]
length = [[0] * (ly + 1) for _ in range(lx + 1)]
prev = [[0b00] * (ly + 1) for _ in range(lx + 1)]

for i_x in range(lx):
    for i_y in range(ly):
        if x[i_x] == y[i_y]:
            length[i_x+1][i_y+1] = length[i_x][i_y] + 1
            chars[i_x+1][i_y+1] = x[i_x]
            prev[i_x+1][i_y+1] = 0b11
        elif length[i_x+1][i_y] > length[i_x][i_y+1]:
            length[i_x+1][i_y+1] = length[i_x+1][i_y]
            prev[i_x+1][i_y+1] = 0b01
        else:
            length[i_x+1][i_y+1] = length[i_x][i_y+1]
            prev[i_x+1][i_y+1] = 0b10

lcs = [''] * length[-1][-1]
i_x, i_y = lx, ly
i = 1
while i_x * i_y:
    if prev[i_x][i_y] == 0b11:
        lcs[-i] = chars[i_x][i_y]
        i += 1
    i_x, i_y = i_x - ((prev[i_x][i_y] & 0b10) >> 1), i_y - (prev[i_x][i_y] & 0b01)

print(''.join(lcs))


Fixed submission:
x = input()
y = input()
lx = len(x)
ly = len(y)

chars = [[''] * (ly + 1) for _ in range(lx + 1)]
length = [[0] * (ly + 1) for _ in range(lx + 1)]
prev = [[0b00] * (ly + 1) for _ in range(lx + 1)]

for i_x in range(lx):
    for i_y in range(ly):
        if x[i_x] == y[i_y]:
            length[i_x+1][i_y+1] = length[i_x][i_y] + 1
            chars[i_x+1][i_y+1] = x[i_x]
            prev[i_x+1][i_y+1] = 0b11
        elif length[i_x+1][i_y] > length[i_x][i_y+1]:
            length[i_x+1][i_y+1] = length[i_x+1][i_y]
            prev[i_x+1][i_y+1] = 0b01
        else:
            length[i_x+1][i_y+1] = length[i_x][i_y+1]
            prev[i_x+1][i_y+1] = 0b10

lcs = [''] * length[-1][-1]
i_x, i_y = lx, ly
i = 1
while i_x and i_y:
    if prev[i_x][i_y] == 0b11:
        lcs[-i] = chars[i_x][i_y]
        i += 1
    i_x, i_y = i_x - ((prev[i_x][i_y] & 0b10) >> 1), i_y - (prev[i_x][i_y] & 0b01)

print(''.join(lcs))

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

lcs = [[''] * (len(y) + 1) for _ in range(len(x) + 1)]
for i_x in range(len(x)):
    for i_y in range(len(y)):
        if x[i_x] == y[i_y]:
            lcs[i_x+1][i_y+1] = lcs[i_x][i_y] + x[i_x]
        elif len(lcs[i_x+1][i_y]) > len(lcs[i_x][i_y+1]):
            lcs[i_x+1][i_y+1] = lcs[i_x+1][i_y]
        else:
            lcs[i_x+1][i_y+1] = lcs[i_x][i_y+1]

print(lcs[-1][-1])


Fixed submission:
x = input()
y = input()
lx = len(x)
ly = len(y)

chars = [[''] * (ly + 1) for _ in range(lx + 1)]
length = [[0] * (ly + 1) for _ in range(lx + 1)]
prev = [[0b00] * (ly + 1) for _ in range(lx + 1)]

for i_x in range(lx):
    for i_y in range(ly):
        if x[i_x] == y[i_y]:
            length[i_x+1][i_y+1] = length[i_x][i_y] + 1
            chars[i_x+1][i_y+1] = x[i_x]
            prev[i_x+1][i_y+1] = 0b11
        elif length[i_x+1][i_y] > length[i_x][i_y+1]:
            length[i_x+1][i_y+1] = length[i_x+1][i_y]
            prev[i_x+1][i_y+1] = 0b01
        else:
            length[i_x+1][i_y+1] = length[i_x][i_y+1]
            prev[i_x+1][i_y+1] = 0b10

lcs = [''] * length[-1][-1]
i_x, i_y = lx, ly
i = 1
while i_x and i_y:
    if prev[i_x][i_y] == 0b11:
        lcs[-i] = chars[i_x][i_y]
        i += 1
    i_x, i_y = i_x - ((prev[i_x][i_y] & 0b10) >> 1), i_y - (prev[i_x][i_y] & 0b01)

print(''.join(lcs))