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LeetCode Binary Tree Level Order Traversal II
Given a binary tree, return the bottom-up level order traversal of its nodes‘ values. (ie, from left to right, level by level from leaf to root).
For example:
Given binary tree {3,9,20,#,#,15,7},
3 / 9 20 / 15 7
return its bottom-up level order traversal as:
[ [15,7], [9,20], [3]]
1 /** 2 * Definition for binary tree 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */10 public class Solution {11 public List<List<Integer>> levelOrderBottom(TreeNode root) {12 LinkedList<List<Integer>> resList= new LinkedList<>();13 14 if (root==null) {15 return resList;16 }17 18 Deque<TreeNode> visitDeque=new LinkedList<>();19 List<Integer> currList;20 visitDeque.add(root);21 int count=1;22 int level=0;23 while (!visitDeque.isEmpty()) {24 level=0;25 currList=new ArrayList<Integer>();26 for (int i = 0; i < count; i++) {27 TreeNode node=visitDeque.pop();28 currList.add(node.val);29 if (node.left != null) {30 ++level;31 visitDeque.add(node.left);32 }33 if (node.right != null) {34 ++level;35 visitDeque.add(node.right);36 }37 }38 count=level;39 resList.addFirst(currList);40 }41 return resList;42 }43 }
LeetCode Binary Tree Level Order Traversal II
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