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Populating Next Right Pointers in Each Node
Given a binary tree
struct TreeLinkNode { TreeLinkNode *left; TreeLinkNode *right; TreeLinkNode *next; }
Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL
.
Initially, all next pointers are set to NULL
.
Note:
- You may only use constant extra space.
- You may assume that it is a perfect binary tree (ie, all leaves are at the same level, and every parent has two children).
For example,
Given the following perfect binary tree,
1 / 2 3 / \ / 4 5 6 7
After calling your function, the tree should look like:
1 -> NULL / 2 -> 3 -> NULL / \ / 4->5->6->7 -> NULL
要将原来的TreeNode增加一个next指针 指向其同层的下一个 很明显地想到是用层序遍历的方法 代码如下:
/** * Definition for binary tree with next pointer. * public class TreeLinkNode { * int val; * TreeLinkNode left, right, next; * TreeLinkNode(int x) { val = x; } * } */ public class Solution { public void connect(TreeLinkNode root) { if(root==null) return ; int count=1; int level=0; Queue<TreeLinkNode> que =new LinkedList<TreeLinkNode>(); que.offer(root); while(que.isEmpty()!=true){ level=0; for(int i=0;i<count;i++){ root=que.peek(); que.poll(); if(i<count-1){ root.next=que.peek(); }else{ root.next=null; } if(root.left!=null){ que.offer(root.left); que.offer(root.right); level++; level++; } } count=level; } } }原来题中要求的是空间复杂度为0(1) 但遍历的话空间复杂度为O(log N)上面方法不满足要求 从例子来看 每一层的next设置都可以根据自身和上一层的结果来设置 所以采用递归即可 代码如下:
public class Solution { public void connect(TreeLinkNode root) { if(root==null)return ; if(root.left!=null){ root.left.next=root.right; } if(root.right!=null&&root.next!=null){ root.right.next=root.next.left; }else{ if(root.right!=null){ root.right.next=null; } } connect(root.left); connect(root.right); } }
Populating Next Right Pointers in Each Node
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