62、剑指offer--二叉搜索树的第k个结点

 1 /*
 2 struct TreeNode {
 3     int val;
 4     struct TreeNode *left;
 5     struct TreeNode *right;
 6     TreeNode(int x) :
 7             val(x), left(NULL), right(NULL) {
 8     }
 9 };
10 */
11 class Solution {
12 public:
13     //实现中序遍历,对于二叉搜索树中序遍历是按节点从小到大排序
14     TreeNode *KthNodeCore(TreeNode *root, int &k)//注意此处k为引用，因为在操作过程中k改变
15     {
16         TreeNode *target = NULL;
17         if(root->left != NULL)
18         {
19             target = KthNodeCore(root->left,k);
20         }
21         if(target == NULL)//无左节点且还未找到，返回其叶子节点的父节点，k--
22         {
23             if(k == 1)
24                 target = root;
25             k--;
26         }
27         if(target == NULL && root->right != NULL)//找右结点
28         {
29             target = KthNodeCore(root->right,k);
30         }
31         return target;
32     }
33     TreeNode* KthNode(TreeNode* pRoot, int k)
34     {
35         if(pRoot == NULL || k == 0)
36             return NULL;
37         return KthNodeCore(pRoot,k);
38     }
39 };