Full binary tree / true binary tree / complete binary tree~

• True binary tree ： The degree of all nodes is 0 or 2
  
• Full binary tree ： The degree of all nodes is 0 or 2 , And all leaf nodes are on the last layer
  nature ： The first i Number of nodes in the layer ：2 ^i-1
              Number of leaf nodes ：2 ^h-1
              Sum up points ：n = 2 ⁰ + 2 ¹ + 2 ² … + 2 ^h-1 =2 ^h -1
              Height ：h = log₂(n+1)
  
• Perfect binary tree ： Leaf nodes only appear in the last two layers , And the leaf nodes of the last layer are aligned to the left
  nature ： Degree is 1 The node has only the left subtree
              Degree is 1 The node of either 1 individual , Or 0 individual
              A binary tree with the same number of nodes , The height of a complete binary tree is the smallest
              Suppose the height of a complete binary tree is h , So at least there is 2 ^h-1 Nodes , At most 2 ^h -1 Nodes .
  

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notes ： A full binary tree must be a real binary tree , True binary trees are not necessarily full of binary trees . A full binary tree must be a complete binary tree , A complete binary tree is not necessarily a full binary tree