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class Solution {
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  public boolean isValidSerialization(String preorder) {
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    String[] strs = preorder.split(",");
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    // In starting we have one vacany for root
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    int vacancy = 1;
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    for (String str : strs) {
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      if (--vacancy < 0) return false;
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      // whenever we encounter a new node vacancy decreases by 1 and  left and right two vacancy for
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      //                   that node will added in total
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      if (!str.equals("#")) vacancy += 2;
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    }
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    return vacancy == 0;
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  }
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}