leetcode二叉树-1302. 层数最深叶子节点的和

考点 层序遍历

package bi++narytree.deepestLeavesSum;

i++mport binarytree.untils.TreeNode;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

/**
* 1302. 层数最深叶子节点的和
* 给你一棵二叉树的根节点 root 请你返回 层数最深的叶子节点的和 。
* <p>
* <p>
* <p>
* 示例 1:
* <p>
* <p>
* <p>
* 输入:root = [1,2,3,4,5,null,6,7,null,null,null,null,8]
* 输出:15
* 示例 2:
* <p>
* 输入:root = [6,7,8,2,7,1,3,9,null,1,4,null,null,null,5]
* 输出:19
* <p>
* <p>
* 提示:
* <p>
* 树中节点数目在范围 [1, 104] 之间。
* 1 <= Node.val <= 100
*/
public class deepestLeavesSum {
/**
* 层序遍历
* @param root
* @return
*/
public static int deepestLeavesSum(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
levelOrder(root, res);
List<Integer> list = res.get(res.size() - 1);
int sum = 0;
for (int i = 0; i < list.size(); i++) {
sum += list.get(i);
}
return sum;
}

private static List<Listi++<4<Integer>> levelOrder(TreeNode root, List<List<Integer>> res) {
Queue<TreeNode> queue = new LinkedList<>();
queue.add(root);
while (!queue.isEmpty()) {
int size = queue.size();
List<Integer> list = new ArrayList<>();
for (int i = 0; i < size; i++) {
TreeNode treeNode = queue.poll();
if (treeNode.left != null) {
queue.add(treeNode.left);
}
if (treeNode.right != null) {
queue.add(treeNode.right);
}
list.add(treeNode.val);
}
if (list.size() != 0) {
res.add(list);
}
}
return res;
}
}

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