题解 | #二叉搜索树的第k个结点#

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};
*/
class Solution {
public:
    TreeNode* KthNode(TreeNode* pRoot, int k) {
        if(!pRoot || k == 0) return 0;
        stack<TreeNode*> stack;
        while(!stack.empty() || pRoot){
            if(pRoot){
                //当前节点非空则找左孩子
                stack.push(pRoot);
                pRoot = pRoot->left;
            }else{
                //为空则出栈一个元素，找该元素的右孩子
                pRoot = stack.top();
                stack.pop();
                if(--k == 0){
                    return pRoot;
                }
                pRoot = pRoot->right;
            }
        }
        return NULL;
    }

    
};