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Populating Next Right Pointers in Each Node II

2024-07-18 15:47:43   225人阅读

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,

         1
       /        2    3
     / \        4   5    7

After calling your function, the tree should look like:

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

使用一个队列保存当前节点和当前层号，prev保存这个节点的前一个节点，如果节点属于同一层，则prev的next指向队列的头元素。

层次遍历

Have you been asked this question in an interview? 
/**
 * 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) {
        if(!root) return;
        queue< pair<TreeLinkNode*,int> > q;
        q.push(pair<TreeLinkNode*,int>(root,0));
        pair<TreeLinkNode* ,int> prev;
        while(!q.empty()){
            pair<TreeLinkNode*,int> temp=q.front();
            q.pop();
            if(prev.first!=NULL&& prev.second==temp.second)
                prev.first->next=temp.first;
            prev=make_pair(temp.first,temp.second);
            if(temp.first->left) q.push(pair<TreeLinkNode*,int>(temp.first->left,temp.second+1));
            if(temp.first->right) q.push(pair<TreeLinkNode*,int>(temp.first->right,temp.second+1));
        }
    }
};


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