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838. Push Dominoes 👍

  • Time: $O(n)$
  • Space: $O(n)$
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class Solution {
 public:
  string pushDominoes(string dominoes) {
    int L = -1;
    int R = -1;

    for (int i = 0; i <= dominoes.length(); ++i)
      if (i == dominoes.length() || dominoes[i] == 'R') {
        if (L < R)
          while (R < i)
            dominoes[R++] = 'R';
        R = i;
      } else if (dominoes[i] == 'L') {
        if (R < L || L == -1 && R == -1) {
          if (L == -1 && R == -1)
            ++L;
          while (L < i)
            dominoes[L++] = 'L';
        } else {
          int l = R + 1;
          int r = i - 1;
          while (l < r) {
            dominoes[l++] = 'R';
            dominoes[r--] = 'L';
          }
        }
        L = i;
      }

    return dominoes;
  }
};
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class Solution {
  public String pushDominoes(String dominoes) {
    char[] s = dominoes.toCharArray();
    int L = -1;
    int R = -1;

    for (int i = 0; i <= dominoes.length(); ++i)
      if (i == dominoes.length() || s[i] == 'R') {
        if (L < R)
          while (R < i)
            s[R++] = 'R';
        R = i;
      } else if (s[i] == 'L') {
        if (R < L || L == -1 && R == -1) {
          if (L == -1 && R == -1)
            ++L;
          while (L < i)
            s[L++] = 'L';
        } else {
          int l = R + 1;
          int r = i - 1;
          while (l < r) {
            s[l++] = 'R';
            s[r--] = 'L';
          }
        }
        L = i;
      }

    return new String(s);
  }
}
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class Solution:
  def pushDominoes(self, dominoes: str) -> str:
    ans = list(dominoes)
    L = -1
    R = -1

    for i in range(len(dominoes) + 1):
      if i == len(dominoes) or dominoes[i] == 'R':
        if L < R:
          while R < i:
            ans[R] = 'R'
            R += 1
        R = i
      elif dominoes[i] == 'L':
        if R < L or (L, R) == (-1, -1):
          if (L, R) == (-1, -1):
            L += 1
          while L < i:
            ans[L] = 'L'
            L += 1
        else:
          l = R + 1
          r = i - 1
          while l < r:
            ans[l] = 'R'
            ans[r] = 'L'
            l += 1
            r -= 1
        L = i

    return ''.join(ans)
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