[LeetCode]Populating Next Right Pointers in Each Node

最新推荐文章于 2021-09-24 12:05:40 发布

原创最新推荐文章于 2021-09-24 12:05:40 发布 · 1.2k 阅读

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本文介绍了一种使用C++实现的二叉树链接节点连接算法，包括节点遍历、链接当前节点的左右子节点以及下一层节点的初始化。

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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
		while(root)
		{
			TreeLinkNode* nextLevel = NULL;//first node in next level, eg. first child in current level 
			TreeLinkNode* prevChild = NULL;//previous node in child level, eg. link previous child's next to current child
			for(; root; root = root->next)//current level
			{
				if(root->left)
				{
					if(!nextLevel)
						nextLevel = root->left;
					if(prevChild)
						prevChild->next = root->left;
					prevChild = root->left;
				}
				if(root->right)
				{
					if(!nextLevel)
						nextLevel = root->right;
					if(prevChild)
						prevChild->next = root->right;
					prevChild = root->right;
				}
			}//end of level traverse
			root = nextLevel;
		}
    }
};

second time

/**
 * 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 ;
        root->next = NULL;
        TreeLinkNode* prevHead = root;
        while(prevHead != NULL)
        {
            TreeLinkNode* cur = prevHead;
            TreeLinkNode* prev = NULL;
            while(cur != NULL)
            {
                if(prev != NULL) prev->next = cur->left;//... 
                if(cur->left != NULL) cur->left->next = cur->right, prev = cur->right;//full tree
                else break;//...
                cur = cur->next;
            }
            if(prev != NULL) prev->next = NULL;
            prevHead = prevHead->left;//...
        }
    }
};