leetcode刷题，总结，记录，备忘114

leetcode114 Flatten Binary Tree to Linked List

Given a binary tree, flatten it to a linked list in-place.

For example,
Given

         1
        / \
       2   5
      / \   \
     3   4   6

The flattened tree should look like:

   1
    \
     2
      \
       3
        \
         4
          \
           5
            \
             6

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这个题目，很简单，，，简单的先序遍历二叉树，然后把节点全连在右子树上就行了。

/**
 * 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;
        }
        
        stack<TreeNode *> st;
        st.push(root);
        vector<TreeNode *> vt;
        
        while (!st.empty())
        {
            TreeNode * t = st.top();
            st.pop();
            vt.push_back(t);
            
            if (t->right)
            {
               st.push(t->right); 
            }
            
            if (t->left)
            {
                st.push(t->left);
            }
        }
        
        for (int i = vt.size() - 1; i >= 0; --i)
        {
            if (i == vt.size() - 1)
            {
                vt[i]->right = NULL;
                vt[i]->left = NULL;
            }
            else
            {
                vt[i]->right = vt[i + 1];
                vt[i]->left = NULL;
            }
        }
    }
};