LeetCode 116. 填充每个节点的下一个右侧节点指针
给定一个完美二叉树,其所有叶子节点都在同一层,每个父节点都有两个子节点。二叉树定义如下:
struct Node {
int val;
Node *left;
Node *right;
Node *next;
}
填充它的每个 next 指针,让这个指针指向其下一个右侧节点。如果找不到下一个右侧节点,则将 next 指针设置为 NULL。
初始状态下,所有 next 指针都被设置为 NULL。
示例:
输入:{"$id":"1","left":{"$id":"2","left":{"$id":"3","left":null,"next":null,"right":null,"val":4},"next":null,"right":{"$id":"4","left":null,"next":null,"right":null,"val":5},"val":2},"next":null,"right":{"$id":"5","left":{"$id":"6","left":null,"next":null,"right":null,"val":6},"next":null,"right":{"$id":"7","left":null,"next":null,"right":null,"val":7},"val":3},"val":1}
输出:{"$id":"1","left":{"$id":"2","left":{"$id":"3","left":null,"next":{"$id":"4","left":null,"next":{"$id":"5","left":null,"next":{"$id":"6","left":null,"next":null,"right":null,"val":7},"right":null,"val":6},"right":null,"val":5},"right":null,"val":4},"next":{"$id":"7","left":{"$ref":"5"},"next":null,"right":{"$ref":"6"},"val":3},"right":{"$ref":"4"},"val":2},"next":null,"right":{"$ref":"7"},"val":1}
解释:给定二叉树如图 A 所示,你的函数应该填充它的每个 next 指针,以指向其下一个右侧节点,如图 B 所示。
提示:
你只能使用常量级额外空间。
使用递归解题也符合要求,本题中递归程序占用的栈空间不算做额外的空间复杂度。
算法:宽搜(bfs)。我们一层一层来处理,先找到每层左子树的左儿子然后改动指针即可。
/* // Definition for a Node. class Node { public: int val; Node* left; Node* right; Node* next; Node() {} Node(int _val, Node* _left, Node* _right, Node* _next) { val = _val; left = _left; right = _right; next = _next; } }; */ class Solution { public: Node* connect(Node* root) { if(!root)return NULL; auto cur=root; while(cur->left){ for(auto p=cur;p;p=p->next){ p->left->next=p->right; if(p->next)p->right->next=p->next->left; else p->right->next=NULL; } cur=cur->left; } return root; } };