[leetcode-二叉树层次遍历并统计每层节点数]--102. Binary Tree Level Order Traversal
2017-02-09 13:22
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Question 102. Binary Tree Level Order Traversal
Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).
For example:
Given binary tree [3,9,20,null,null,15,7],
return its level order traversal as:
二叉树的层次遍历并统计每层结点的数量
解决: 这里使用FIFO队列来实现,对于统计每层结点的统计,根据层次遍历时队列的特性可以直接获取并存入队列。
实现源码如下:
测试用例:
运行结果:
本文完整代码github地址:
https://github.com/leetcode-hust/leetcode/blob/master/louyuting/src/leetcode/Question102.java
Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).
For example:
Given binary tree [3,9,20,null,null,15,7],
3 / \ 9 20 / \ 15 7
return its level order traversal as:
[ [3], [9,20], [15,7] ]
二叉树的层次遍历并统计每层结点的数量
解决: 这里使用FIFO队列来实现,对于统计每层结点的统计,根据层次遍历时队列的特性可以直接获取并存入队列。
实现源码如下:
/** * 二叉树的层次遍历 * 使用队列实现 * @param root * @return */ public static List<List<Integer>> levelOrder(TreeNode root) { Queue<TreeNode> queue = new LinkedList<TreeNode>();//队列里面存放结点 List<List<Integer>> result = new ArrayList<List<Integer>>(); //如果为空树就直接返回 if(root == null){ return result; } queue.offer(root);//根节点先入队 //只要队列非空就一直循环; while (!queue.isEmpty()){ int levelNum = queue.size();//获取当前层的节点数. List<Integer> subList = new ArrayList<>(); //遍历当前层结点 for(int i=0; i<levelNum; i++){ //队首出队并将value加入子list TreeNode node = queue.poll(); subList.add(node.val); //将非空左右子树加入queue if(node.left != null){//如果队首的左结点不为空就把左结点入队 queue.offer(node.left); } if(node.right != null){//如果队首的右结点不为空就把右结点入队 queue.offer(node.right); } } result.add(subList);//添加一层 } return result; }
测试用例:
public static void main(String[] args) { TreeNode root = new TreeNode(3); root.left = new TreeNode(9); root.right = new TreeNode(20); root.right.left = new TreeNode(15); root.right.right = new TreeNode(7); List<List<Integer>> res = Question102.levelOrder(root); for(List<Integer> is : res){ for(Integer i : is){ System.out.print(i + ", "); } System.out.println(); } }
运行结果:
3, 9, 20, 15, 7,
本文完整代码github地址:
https://github.com/leetcode-hust/leetcode/blob/master/louyuting/src/leetcode/Question102.java
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