Tree - 331. Verify Preorder Serialization of a Binary Tree

331. Verify Preorder Serialization of a Binary Tree

One way to serialize a binary tree is to use pre-order traversal. When we encounter a non-null node, we record the node's value. If it is a null node, we record using a sentinel value such as #.

     _9_
    /   
   3     2
  /    / 
 4   1  #  6
/  /    / 
# # # #   # #

For example, the above binary tree can be serialized to the string "9,3,4,#,#,1,#,#,2,#,6,#,#", where # represents a null node.

Given a string of comma separated values, verify whether it is a correct preorder traversal serialization of a binary tree. Find an algorithm without reconstructing the tree.

Each comma separated value in the string must be either an integer or a character '#' representing null pointer.

You may assume that the input format is always valid, for example it could never contain two consecutive commas such as "1,,3".

思路：

读取到的结构只要符合二叉树性质而且不会在未读完之前就满足leaves = nodes + 1（完整的二叉树）即可

代码：

go：

func isValidSerialization(preorder string) bool {

    leaves := 0
    node := 0
    pres := strings.Split(preorder,",")
	for i, s := range pres {
		if s == "#" {
			leaves++
		} else {
			node++
		}
		if leaves > node + 1{
			return false
		}
		if leaves == node + 1 && i < len(pres)- 1 {
			return false
		}
    }
    
	if leaves != node + 1{
		return false
    }
    return true
}