199. Binary Tree Right Side View
摘要：
Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.
Ex...
Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.
Example:
Input: [1,2,3,null,5,null,4] Output: [1, 3, 4] Explanation: 1<--- /\ 23<--- \\ 54<---
難度： medium
題目： 給定二叉樹，想像一下你站在樹的右邊，返回能看到的所有結點，結點從上到下輸出。
思路：層次遍歷，ＢＦＳ
Runtime: 1 ms, faster than 79.74% of Java online submissions for Binary Tree Right Side View.
Memory Usage: 34.7 MB, less than 100.00% of Java online submissions for Binary Tree Right Side View.
/**
* Definition for a binary tree node.
* public class TreeNode {
*int val;
*TreeNode left;
*TreeNode right;
*TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public List<Integer> rightSideView(TreeNode root) {
List<Integer> result = new ArrayList<>();
if (null == root) {
return result;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.add(root);
while (!queue.isEmpty()) {
int qSize = queue.size();
for (int i = 0; i < qSize; i++) {
TreeNode node = queue.poll();
if (node.right != null) {
queue.add(node.right);
}
if (node.left != null) {
queue.add(node.left);
}
if (0 == i) {
result.add(node.val);
}
}
}
return result;
}
}