Q:给定一棵二叉搜索树,请找出其中的第k小的结点。例如, (5,3,7,2,4,6,8) 中,按结点数值大小顺序第三小结点的值为4。
T:
中序遍历,递归:
int count = 0;
public:
TreeNode* KthNode(TreeNode* pRoot, unsigned int k)
{
if(pRoot){
TreeNode *ret = KthNode(pRoot->left, k);
if(ret) return ret;//第k个出现在left里面
if(++count == k) return pRoot;
ret = KthNode(pRoot->right,k);
if(ret) return ret;
}
return nullptr;
}
非递归:
TreeNode *KthNode(TreeNode *pRoot, int k) {
if (pRoot == nullptr)
return nullptr;
stack<TreeNode *> s;
s.push(pRoot);
TreeNode *node = pRoot->left;
while (node || !s.empty()) {
if (node) {
s.push(node);
node = node->left;
} else {
node = s.top();
s.pop();
k--;
if (k == 0) {
return node;
}
node = node->right;
}
}
return nullptr;
}