BinaryTreeLevelOrderTraversal
BinaryTreeLevelOrderTraversal.java 源码
package datastructure.tree.leetcode;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
/**
* @author roseduan
* @time 2020/9/20 1:56 上午
* @description 二叉树的层次遍历
*/
public class BinaryTreeLevelOrderTraversal {
/**
* 广度优先遍历的思想，使用一个队列
*/
public List<List<Integer>> levelOrder(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
if (root == null) {
return res;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.add(root);
while (!queue.isEmpty()) {
int n = queue.size();
List<Integer> list = new ArrayList<>();
for (int i = 0; i < n; i++) {
TreeNode node = queue.poll();
if (node != null) {
list.add(node.val);
if (node.left != null) {
queue.add(node.left);
}
if (node.right != null) {
queue.add(node.right);
}
}
}
res.add(list);
}
return res;
}
public class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int val) { this.val = val; }
TreeNode(int val, TreeNode left, TreeNode right) {
this.val = val;
this.left = left;
this.right = right;
}
}
}
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