二叉树的坡度

二叉树的坡度

/**
 * 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 {
	//坡度值
    int ans = 0;

    public int findTilt(TreeNode root) {
        dfs(root);
        return ans;
    }

    public int dfs(TreeNode node) {
        if (node == null)
            return 0;

        int suml = dfs(node.left);
        int sumr = dfs(node.right);
        ans += Math.abs(suml - sumr);
        //dfs不是计算坡度，而是用于计算图中右边二叉树的数值，所以要加上node.val
        //当前结点的坡度值跟当前的node.val无关，但是父结点的坡度跟node.val有关
        return suml + sumr + node.val;
    }
}