LeetCode 114 Flatten Binary Tree to Linked List

LeetCode 114

Flatten Binary Tree to Linked List

• Problem Description：
  将二叉树节点值用链表存储起来，根据题目给的例子可以看出实际考查的是树的先序遍历。

  具体的题目信息：
  https://leetcode.com/problems/flatten-binary-tree-to-linked-list/description/

• Example:
  
• Solution:

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void flatten(TreeNode* root) {
        if (root == NULL) return;
        TreeNode* head = root;
        TreeNode* p = root;
        queue<TreeNode*> tree;
        stack<TreeNode*> node;
        while(p || !node.empty()) {
            while(p) {
                node.push(p);
                tree.push(p);
                p = p->left;
            }
            if (!node.empty()) {
                p = node.top();
                node.pop();
                p = p->right;
            }
        }
        p = head;
        if (!tree.empty())
            tree.pop();
        while(!tree.empty()) {
            TreeNode* q = new TreeNode(tree.front()->val);
            tree.pop();
            p->right = q;
            p->left = NULL;
            p = q;
        }
        p->right = NULL;
        p->left = NULL;
        root = head;
    }
};