lintcode-453-将二叉树拆成链表
453-将二叉树拆成链表
将一棵二叉树按照前序遍历拆解成为一个假链表。所谓的假链表是说,用二叉树的 right 指针,来表示链表中的 next 指针。
注意事项
不要忘记将左儿子标记为 null,否则你可能会得到空间溢出或是时间溢出。
样例
挑战
不使用额外的空间耗费。
标签
二叉树 深度优先搜索
方法一
使用栈保存暂时无法插入到链表的节点
code
/**
* Definition of TreeNode:
* class TreeNode {
* public:
* int val;
* TreeNode *left, *right;
* TreeNode(int val) {
* this->val = val;
* this->left = this->right = NULL;
* }
* }
*/
class Solution {
public:
/*
* @param root: a TreeNode, the root of the binary tree
* @return:
*/
void flatten(TreeNode * root) {
// write your code here
if (root == NULL) {
return ;
}
stack<TreeNode *>stack;
TreeNode * node = root;
bool isContinue = true;
while (isContinue) {
if (node->left != NULL && node->right != NULL) {
stack.push(node->right);
node->right = node->left;
node->left = NULL;
}
else if (node->left != NULL && node->right == NULL) {
node->right = node->left;
node->left = NULL;
}
else if (node->left == NULL && node->right == NULL) {
if (!stack.empty()) {
node->right = stack.top();
stack.pop();
}
else {
isContinue = false;
}
}
node = node->right;
}
}
};
方法二
使用递归
code
/**
* Definition of TreeNode:
* class TreeNode {
* public:
* int val;
* TreeNode *left, *right;
* TreeNode(int val) {
* this->val = val;
* this->left = this->right = NULL;
* }
* }
*/
class Solution {
public:
/*
* @param root: a TreeNode, the root of the binary tree
* @return:
*/
void flatten(TreeNode * root) {
// write your code here
if (root == NULL) {
return;
}
switchToLink(root);
}
TreeNode* switchToLink(TreeNode* root) {
if (root == NULL) {
return NULL;
}
TreeNode* left = switchToLink(root->left);
TreeNode* right = switchToLink(root->right);
if (left != NULL) {
left->right = root->right;
root->right = root->left;
}
root->left = NULL;
if (right != NULL) {
return right;
}
else if (left != NULL) {
return left;
}
else {
return root;
}
}
};