331. Verify Preorder Serialization of a Binary Tree

[huimeich]

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:
"9,3,4,#,#,1,#,#,2,#,6,#,#"
Return true

Example 2:
"1,#"
Return false

Example 3:
"9,#,#,1"
Return false

[huimeich]

public class Solution {
    public boolean isValidSerialization(String preorder) {
        int count = 1;
        int i;
        String[] arr = preorder.split(",");
        for (i = 0; i < arr.length; i++) {
            if (arr[i].equals("#")) count--;
            else count++;
            System.out.println(arr[i] + " count: " + count);
            if (count == 0) break;
        }
        if (count != 0 || i < arr.length - 1) return false;
        return true;
    }
}