[leetcode-563-Binary Tree Tilt]

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

int sumOfTree(TreeNode* root)
{
    if(root == NULL) return ;
    if(root -> left == NULL && root  -> right == NULL) return root->val;
    return sumOfTree(root->left) + sumOfTree(root->right) + root->val;
}
int getTilt(TreeNode* root)
{
    if(root == NULL || (root->left == NULL)&&(root->right == NULL)) return ;
    return abs(sumOfTree(root->left) - sumOfTree(root->right) ) ;
}
int findTilt(TreeNode* root)
{
    if(root == NULL || (root->left == NULL)&&(root->right == NULL)) return ;

    int left = findTilt(root->left);
    int right = findTilt(root->right);
    return left + right + getTilt(root);
}