LeetCode link

first thought

  • BFS. Two queue to iterate, update the result when finish one level.

solution

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
class Solution {
    public int findBottomLeftValue(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        int result = root.val;
        while (!queue.isEmpty()) {
            Queue<TreeNode> queue2 = new LinkedList<>();
            TreeNode node = queue.peek();
            result = node.val;
            while (!queue.isEmpty()) {
                node = queue.poll();
                if (node.left != null) {
                    queue2.add(node.left);
                }
                if (node.right != null) {
                    queue2.add(node.right);
                }
            }
            queue = queue2;
        }
        return result;
    }
}