LeetCode:Flatten Binary Tree to Linked List

题目链接

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

分析：按照树的先序遍历顺序把节点串联起来即可，代码如下                                                           本文地址

/**
 * Definition for binary tree
 * struct TreeNode {
 * int val;
 * TreeNode *left;
 * TreeNode *right;
 * TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void flatten(TreeNode *root) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(root == NULL)return ;
        stack<TreeNode *> S;
        S.push(root);
        TreeNode *pre = NULL;
        while(S.empty() == false)
        {
            TreeNode *p = S.top();
            S.pop();
            if(pre != NULL)
            {
                pre->right = p;
                pre->left = NULL;
            }
            if(p->right)S.push(p->right);
            if(p->left)S.push(p->left);
            pre = p;
        }
        pre->left = NULL;
        pre->right = NULL;
    }
};

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