0331. Verify Preorder Serialization of a Binary Tree

331. Verify Preorder Serialization of a Binary Tree#

题目 #

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”.

Example 1:

Input: "9,3,4,#,#,1,#,#,2,#,6,#,#"
Output: true

Example 2:

Input: "1,#"
Output: false

Example 3:

Input: "9,#,#,1"
Output: false

代码 #

package leetcode

import "strings"

func isValidSerialization(preorder string) bool {
nodes, diff := strings.Split(preorder, ","), 1
for _, node := range nodes {
diff--
if diff < 0 {
return false
}
if node != "#" {
diff += 2
}
}
return diff == 0
}

Sep 6, 2020