题解 | #把字符串转换成整数#Java递归

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {
    int num = 0;
    int k;
    TreeNode ans;
    TreeNode KthNode(TreeNode pRoot, int k) {
        if(pRoot == null){
            return null;
        }
        this.k = k;
        helper(pRoot);
        return ans;
    }
    void helper(TreeNode pRoot){
        if(pRoot == null){
            return;
        }
        if(pRoot.left != null){
            helper(pRoot.left);
        }
        num++;
        if(num == k){
            ans = pRoot;
            return;
        }
        if(pRoot.right != null){
            helper(pRoot.right);
        }
    }

}