Formatted question description: https://leetcode.ca/all/563.html

563. Binary Tree Tilt (Easy)

Given the root of a binary tree, return the sum of every tree node's tilt.

The tilt of a tree node is the absolute difference between the sum of all left subtree node values and all right subtree node values. If a node does not have a left child, then the sum of the left subtree node values is treated as 0. The rule is similar if there the node does not have a right child.

 

Example 1:

Input: root = [1,2,3]
Output: 1
Explanation: 
Tilt of node 2 : |0-0| = 0 (no children)
Tilt of node 3 : |0-0| = 0 (no children)
Tile of node 1 : |2-3| = 1 (left subtree is just left child, so sum is 2; right subtree is just right child, so sum is 3)
Sum of every tilt : 0 + 0 + 1 = 1

Example 2:

Input: root = [4,2,9,3,5,null,7]
Output: 15
Explanation: 
Tilt of node 3 : |0-0| = 0 (no children)
Tilt of node 5 : |0-0| = 0 (no children)
Tilt of node 7 : |0-0| = 0 (no children)
Tilt of node 2 : |3-5| = 2 (left subtree is just left child, so sum is 3; right subtree is just right child, so sum is 5)
Tilt of node 9 : |0-7| = 7 (no left child, so sum is 0; right subtree is just right child, so sum is 7)
Tilt of node 4 : |(3+5+2)-(9+7)| = |10-16| = 6 (left subtree values are 3, 5, and 2, which sums to 10; right subtree values are 9 and 7, which sums to 16)
Sum of every tilt : 0 + 0 + 0 + 2 + 7 + 6 = 15

Example 3:

Input: root = [21,7,14,1,1,2,2,3,3]
Output: 9

 

Constraints:

  • The number of nodes in the tree is in the range [0, 104].
  • -1000 <= Node.val <= 1000

Related Topics:
Tree, Depth-first Search, Recursion

Similar Questions:

Solution 1.

// OJ: https://leetcode.com/problems/binary-tree-tilt/

// Time: O(N)
// Space: O(H)
class Solution {
    int ans = 0;
    int dfs(TreeNode *root) {
        if (!root) return 0;
        int L = dfs(root->left), R = dfs(root->right);
        ans += abs(L - R);
        return L + R + root->val;
    }
public:
    int findTilt(TreeNode* root) {
        dfs(root);
        return ans;
    }
};

Java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int findTilt(TreeNode root) {
        if (root == null)
            return 0;
        int leftTilt = findTilt(root.left), rightTilt = findTilt(root.right);
        int leftSum = nodeValuesSum(root.left), rightSum = nodeValuesSum(root.right);
        int rootTilt = Math.abs(leftSum - rightSum);
        return leftTilt + rightTilt + rootTilt;
    }

    public int nodeValuesSum(TreeNode root) {
        if (root == null)
            return 0;
        else
            return root.val + nodeValuesSum(root.left) + nodeValuesSum(root.right);
    }
}

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