题解 | #二叉搜索树的第k个节点#

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param proot TreeNode类 
     * @param k int整型 
     * @return int整型
     */
    public int KthNode (TreeNode proot, int k) {
        // write code here
        if(proot == null){
            return -1;
        }
        int i = 0;
        while(proot != null){
            if(proot.left != null){
                TreeNode node = proot.left;
                while(node.right != null && node.right != proot){
                    node = node.right;
                }
                if(node.right != proot){
                    node.right = proot;
                    proot = proot.left;
                }else{
                    node.right = null;
                    if((++i) == k){
                        return proot.val;
                    }
                    proot = proot.right;
                }
            }else{
                if((++i) == k){
                        return proot.val;
                    }
                  proot = proot.right;
            }
        }
        return -1;
    }
}