public class BinaryTreeTilt {

int tilt = 0;

/**

* 这题意思是遍历所有结点，对每个节点计算tilt，然后求和

* 对于给定root，其tilt为左子树所有节点的和与右子树所有结点的和的差的绝对值

*/

public int findTilt(TreeNode root) {

helper(root);

return tilt;

}

private int helper(TreeNode root) {

if (root == null) {

return 0;

}

int left = helper(root.left);

int right = helper(root.right);

tilt += Math.abs(left - right);

return left + right + root.val;

}

}