Populating Next Right Pointers in Each Node II

最新推荐文章于 2021-01-29 16:34:55 发布

IIcyZhao

最新推荐文章于 2021-01-29 16:34:55 发布

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分类专栏： LeetCode记录

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本文探讨了如何仅使用常数额外空间，在任意二叉树中填充每个节点的Next指针，使其指向同一层的下一个节点。提供了一个递归解决方案，并详细解释了实现细节。

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Follow up for problem "Populating Next Right Pointers in Each Node".

What if the given tree could be any binary tree? Would your previous solution still work?

Note:

You may only use constant extra space.

For example,
Given the following binary tree,

After calling your function, the tree should look like:

         1 -> NULL
       /  \
      2 -> 3 -> NULL
     / \    \
    4-> 5 -> 7 -> NULL

/**
 * Definition for binary tree with next pointer.
 * struct TreeLinkNode {
 *  int val;
 *  TreeLinkNode *left, *right, *next;
 *  TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {}
 * };
 */
class Solution {
public:
    void connect(TreeLinkNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (root == NULL) {
            return;
        }
        
        TreeLinkNode *next = root->next;
        while (next != NULL && next->left == NULL && next->right == NULL) {
            next = next->next;
        }
        if (next) {
            if (next->left) {
                next = next->left;
            } else {
                next = next->right;
            }
        }
        
        if (root->left) {
            if (root->left->next != NULL) {
                return;
            }
            if (root->right) {
               root->left->next = root->right;
            } else {
              root->left->next = next;
            }
        }
        
        if (root->right) {
            if (root->right->next != NULL) {
                return;
            }
            root->right->next = next;
        }
        connect(root->next);
        connect(root->left);
        connect(root->right);
    }
};