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_0107_BinaryTreeLevelOrderTraversalII.java
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_0107_BinaryTreeLevelOrderTraversalII.java
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package com.diguage.algorithm.leetcode;
import com.diguage.algorithm.util.PrintUtils;
import com.diguage.algorithm.util.TreeNode;
import java.util.*;
import static com.diguage.algorithm.util.TreeNodeUtils.buildTree;
import static java.util.Arrays.asList;
/**
* = 107. Binary Tree Level Order Traversal II
*
* https://leetcode.com/problems/binary-tree-level-order-traversal-ii/[Binary Tree Level Order Traversal II - LeetCode]
*
* @author D瓜哥, https://www.diguage.com/
* @since 2020-02-05 23:20
*/
public class _0107_BinaryTreeLevelOrderTraversalII {
/**
* Runtime: 1 ms, faster than 86.28% of Java online submissions for Binary Tree Level Order Traversal II.
* Memory Usage: 38.8 MB, less than 5.00% of Java online submissions for Binary Tree Level Order Traversal II.
*/
public List<List<Integer>> levelOrderBottom(TreeNode root) {
if (Objects.isNull(root)) {
return Collections.emptyList();
}
List<List<Integer>> result = new ArrayList<>();
Deque<TreeNode> deque = new LinkedList<>();
deque.addLast(root);
while (!deque.isEmpty()) {
int size = deque.size();
List<Integer> nums = new ArrayList<>(size);
for (int i = 0; i < size; i++) {
TreeNode node = deque.removeFirst();
nums.add(node.val);
if (Objects.nonNull(node.left)) {
deque.addLast(node.left);
}
if (Objects.nonNull(node.right)) {
deque.addLast(node.right);
}
}
result.add(nums);
}
Collections.reverse(result);
return result;
}
public static void main(String[] args) {
_0107_BinaryTreeLevelOrderTraversalII solution = new _0107_BinaryTreeLevelOrderTraversalII();
List<List<Integer>> r1 = solution.levelOrderBottom(buildTree(asList(3, 9, 20, null, null, 15, 7)));
PrintUtils.printMatrix(r1);
}
}