leetcode:116. 填充每个节点的下一个右侧节点指针(java树层次遍历bfs)
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2022-05-20 16:12:22
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package LeetCode;
import java.util.LinkedList;
import java.util.Queue;
/*
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。
*/
class Node {
public int val;
public Node left;
public Node right;
public Node next;
public Node() {
}
public Node(int _val, Node _left, Node _right, Node _next) {
val = _val;
left = _left;
right = _right;
next = _next;
}
}
public class Connect {
/*
思路:用层次遍历然后先把第一个取出然后遍历剩余的节点时用next连起来即可
*/
public Node connect(Node root) {
if(root==null) return null;
Queue<Node> queue = new LinkedList<>();
queue.add(root);
while (!queue.isEmpty()) {
int qcount = queue.size();
qcount--;
Node first = queue.poll();
if (first.left != null) {
queue.add(first.left);
}
if (first.right != null) {
queue.add(first.right);
}
while (qcount > 0) {
Node now = queue.poll();
if (now.left != null) {
queue.add(now.left);
}
if (now.right != null) {
queue.add(now.right);
}
first.next = now;
first = first.next;
qcount--;
}
}
return root;
}
public static void main(String[] args) {
Node node4 = new Node(4, null, null, null);
Node node5 = new Node(5, null, null, null);
Node node6 = new Node(6, null, null, null);
Node node7 = new Node(7, null, null, null);
Node node2 = new Node(2, node4, node5, null);
Node node3 = new Node(3, node6, node7, null);
Node node1 = new Node(1, node2, node3, null);
Connect connect = new Connect();
connect.connect(node1);
}
}
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