838. Push Dominoes 推托米诺骨牌

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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.

Given a string "S" representing the initial state. S[i] = 'L', if the i-th domino has been pushed to the left; S[i] = 'R', if the i-th domino has been pushed to the right; S[i] = '.', if the i-th domino has not been pushed.

Return a string representing the final state. 

Example 1:

Input: ".L.R...LR..L.."
Output: "LL.RR.LLRRLL.."

Example 2:

Input: "RR.L"
Output: "RR.L"
Explanation: The first domino expends no additional force on the second domino.

Note:

1. 0 <= N <= 10^5
2. String dominoes contains only 'L', 'R' and '.'

刚出的题，没人写，我来写写看。

'L'代表往左推， 'R'代表往右推，推同时进行。

思路：用idx记录最近出现的R或L，记录出现R后往右推的个数，每次遇到L回填'L'，之前如果是L，从idx开始全部填充为L，之前如果是R，则从idx开始到i结束的中段开始填充L。idx初始化为-1。

代码：

class Solution {
public:
	string pushDominoes(string dominoes) {
		bool with_right = false;
		int right_cnt = 0, idx = -1;
		for (int i = 0; i