题目

解题思路

题解

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    int tilt = 0;
    public int findTilt(TreeNode root) {
        helper(root);
        return tilt;
    }
    public int helper(TreeNode node) {
        if(node == null ) {
            return 0; // 空节点返回0
        }
        int leftSum = helper(node.left); // 左子树之和
        int rightSum = helper(node.right); // 右子树之和
        tilt += Math.abs(leftSum-rightSum); // 总坡度存储在全局变量 tilt 中
        return leftSum + rightSum + node.val; // 返回值是子树之和
    }
}