199. Binary Tree Right Side View

Leetcode Tree Depth-first Search Breadth-first Search

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            <---
 /   \
2     3         <---
 \     \
  5     4       <---

分析

使用深度优先遍历，刚好首先遍历到的就是从右边看见的。

public List<Integer> rightSideView(TreeNode root) {
    List<Integer> list = new ArrayList<>();
    traversal(list, root, 0);
    return list;
}


private void traversal(List<Integer> list, TreeNode root, int height) {
    if (root == null) return;
    if (height == list.size()) list.add(root.val);
    traversal(list, root.right, height + 1);
    traversal(list, root.left, height + 1);
}