[9/27] 838. Push Dominoes
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There are n dominoes in a line, and we place each domino vertically upright. In the beginning, we simultaneously push some of the dominoes either to the left or to the right.
After each second, each domino that is falling to the left pushes the adjacent domino on the left. Similarly, the dominoes falling to the right push their adjacent dominoes standing on the right.
When a vertical domino has dominoes falling on it from both sides, it stays still due to the balance of the forces.
For the purposes of this question, we will consider that a falling domino expends no additional force to a falling or already fallen domino.
You are given a string dominoes representing the initial state where:
dominoes[i] = 'L', if theithdomino has been pushed to the left,dominoes[i] = 'R', if theithdomino has been pushed to the right, anddominoes[i] = '.', if theithdomino has not been pushed.
Return a string representing the final state.
Example 1:
Input: dominoes = "RR.L" Output: "RR.L" Explanation: The first domino expends no additional force on the second domino.
Example 2:
Input: dominoes = ".L.R...LR..L.." Output: "LL.RR.LLRRLL.."
Constraints:
n == dominoes.length1 <= n <= 105dominoes[i]is either'L','R', or'.'.
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Memory Usage: 15.3 MB, less than 98.37% of Python3 online submissions for Push Dominoes.
class Solution:
def pushDominoes(self, dominoes: str) -> str:
dominoes = "L" + dominoes + "R"
prev_idx = 0
ans = ""
for i in range(1, len(dominoes)):
dom_num = i - prev_idx - 1
if dominoes[i] == ".": continue
if dominoes[i] == dominoes[prev_idx]:
ans += dominoes[i] * dom_num
elif dominoes[i] == "L" and dominoes[prev_idx] == "R":
m, d = divmod(dom_num, 2)
ans += "R"*m + "."*d + "L"*m
else:
ans += "." * dom_num
prev_idx = i
ans += dominoes[i]
return ans[:-1]
