[LeetCode] 663. Equal Tree Partition

Problem

Given a binary tree with n nodes, your task is to check if it's possible to partition the tree to two trees which have the equal sum of values after removing exactly one edge on the original tree.

Example 1:

Input:     
    5
   / \
  10 10
    /  \
   2   3

Output: True
Explanation: 
    5
   / 
  10
      
Sum: 15

   10
  /  \
 2    3

Sum: 15

Example 2:

Input:     
    1
   / \
  2  10
    /  \
   2   20

Output: False
Explanation: You can't split the tree into two trees with equal sum after removing exactly one edge on the tree.

Note:
The range of tree node value is in the range of [-100000, 100000].
1 <= n <= 10000

Solution

class Solution {
    Map<Integer, Integer> map = new HashMap<>();
    public boolean checkEqualTree(TreeNode root) {
        if (root == null) return false;
        int total = getTotal(root);
        if (total%2 != 0) return false;
        if (total/2 == 0) return map.getOrDefault(total/2, 0) > 1;
        return map.containsKey(total/2);
    }
    private int getTotal(TreeNode root) {
        if (root == null) return 0;
        int total = root.val+getTotal(root.left)+getTotal(root.right);
        map.put(total, map.getOrDefault(total, 0)+1);
        return total;
    }
}