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binary_tree_level_order_traversal_ii.java
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binary_tree_level_order_traversal_ii.java
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package src.easy;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
/**
* @program: leetcode
* @description: https://leetcode.com/problems/binary-tree-level-order-traversal-ii/
* @author: wqdong
* @create: 2020-01-26 09:45
**/
public class binary_tree_level_order_traversal_ii {
public static class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) {
val = x;
}
}
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);
System.out.println(levelOrderBottom(root));
System.out.println(levelOrderBottom2(root));
}
// Runtime: 2 ms, faster than 11.54% of Java online submissions for Binary Tree Level Order Traversal II.
public static List<List<Integer>> levelOrderBottom(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
if (root == null) {
return res;
}
Queue<TreeNode> q = new LinkedList<>();
q.add(root);
while (!q.isEmpty()) {
int level_size = q.size();
List<Integer> curr_level = new ArrayList<>();
for (int i = 0; i < level_size; i++) {
TreeNode curr_node = q.poll();
curr_level.add(curr_node.val);
if (curr_node.left != null) {
q.add(curr_node.left);
}
if (curr_node.right != null) {
q.add(curr_node.right);
}
}
if (!curr_level.isEmpty()) {
res.add(0, curr_level);
}
}
return res;
}
// Runtime: 0 ms, faster than 100.00% of Java online submissions for Binary Tree Level Order Traversal II.
public static List<List<Integer>> levelOrderBottom2(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
if (root == null) {
return res;
}
levelOrderBottom(root, res, 0);
return res;
}
private static void levelOrderBottom(TreeNode root, List<List<Integer>> res, int height) {
if (root == null) {
return;
}
if (height >= res.size()) {
res.add(0, new ArrayList<Integer>());
}
levelOrderBottom(root.left, res, height + 1);
levelOrderBottom(root.right, res, height + 1);
res.get(res.size() - height - 1).add(root.val);
}
}