一開始想用DP
幹發現怎麼都D不太出來:(
後來發現好像不管先碰ab或先碰ba，最後總共碰的次數都會一樣
(不會因為某個地方選擇碰ba不碰ab，造成後面總共碰的對數少了幾對)
總而言之就變成說
若y>x，就先全碰ba，最後再來處理ab
反之就先全碰ab，最後再來處理ba
大概是這樣
寫得醜醜:(
def maximumGain(self, s: str, x: int, y: int) -> int:
stk = []
score = 0
for c in s:
if x >= y:
if stk and stk[-1] == 'a' and c == 'b':
stk.pop()
score += x
else:
stk.append(c)
else:
if stk and stk[-1] == 'b' and c == 'a':
stk.pop()
score += y
else:
stk.append(c)
stk2 = []
for c in stk:
if stk2 and stk2[-1] == 'a' and c == 'b':
stk2.pop()
score += x
elif stk2 and stk2[-1] == 'b' and c == 'a':
stk2.pop()
score += y
else:
stk2.append(c)
return score