C# 的动态性多态说明

👨‍🏫 参考题解

/**
 * 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 {
    private int ans = 0;

    public int sumNumbers(TreeNode root) {
        dfs(root, 0);
        return ans;
    }
    void dfs(TreeNode node, int x){
        if(node == null){
            return;
        }
        x = x * 10 + node.val;
        if(node.left == node.right)// 叶子节点
        {
            ans += x;
            return;
        }
        dfs(node.left, x);
        dfs(node.right, x);
    }
}