563 Binary Tree Tilt

563. Binary Tree Tilt

1. Question

Given a binary tree, return the tilt of the whole tree.

The tilt of a tree node is defined as the absolute difference between the sum of all left subtree node values and the sum of all right subtree node values. Null node has tilt 0.

The tilt of the whole tree is defined as the sum of all nodes' tilt.

Example:

Input:

         1
       /   \
      2     3

Output:
 1

Explanation:

Tilt of node 2 : 0
Tilt of node 3 : 0
Tilt of node 1 : |2-3| = 1
Tilt of binary tree : 0 + 0 + 1 = 1

Note:

1. The sum of node values in any subtree won't exceed the range of 32-bit integer.

2. All the tilt values won't exceed the range of 32-bit integer.

2. Implementation

(1) Post-order Traversal

class Solution {
    public int findTilt(TreeNode root) {
        int[] tilt = new int[1];
        getSum(root, tilt);
        return tilt[0];
    }

    public int getSum(TreeNode node, int[] tilt) {
        if (node == null) {
            return 0;
        }

        int leftSum = getSum(node.left, tilt);
        int rightSum = getSum(node.right, tilt);

        tilt[0] += Math.abs(leftSum - rightSum);
        return leftSum + rightSum + node.val;
    }
}

3. Time & Space Complexity

Post-order Traversal: 时间复杂度: O(n), 空间复杂度: O(h)