[leetcode]Flatten Binary Tree to Linked List

最新推荐文章于 2020-06-07 20:07:19 发布

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#Flatten Binary Tree

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本文介绍了一种将二叉树结构通过非递归前序遍历的方式转换为链表的方法。此方法适用于原地操作，无需额外的空间。通过对二叉树节点的巧妙调整，确保每个节点的右子节点指向原二叉树前序遍历中的下一个节点。

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Flatten Binary Tree to Linked List

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

For example,
Given

The flattened tree should look like:

Hints:

If you notice carefully in the flattened tree, each node's right child points to the next node of a pre-order traversal.

解题思路：非递归前序遍历的应用改进，左右不空时压右

/**
 * 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 treeToLine(TreeNode *root, stack<TreeNode*> &stn){
        if(root->left == NULL && root->right == NULL){
            if(stn.empty()) return;
            root->right = stn.top(); //栈中还有结点时出栈
            stn.pop();
        }else if(root->left && root->right == NULL){
            root->right = root->left;
        }else if(root->left && root->right){
            stn.push(root->right); //左右都不空时，右子树进栈
            root->right = root->left;
        }
        root->left = NULL;
        treeToLine(root->right, stn);
    }
    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(NULL == root) return;
        stack<TreeNode*> stn;
        treeToLine(root, stn);
    }
};