366. Find Leaves of Binary Tree C#

Example:
Given binary tree

          1
         / \
        2   3
       / \
      4   5

Returns [4, 5, 3], [2], [1].

Explanation:

1. Removing the leaves [4, 5, 3] would result in this tree:

          1
         /
        2

2. Now removing the leaf [2] would result in this tree:

          1

3. Now removing the leaf [1] would result in the empty tree:

          []

Returns [4, 5, 3], [2], [1].

Solution:

Mark tree by level , if it is leave then mark as level 0, then add to the List<List<int>> by level.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public IList<IList<int>> FindLeaves(TreeNode root) {
        IList<IList<int>> result = new List<IList<int>> ();
        LeavesLevel(root, result);
        return result;
    }

    public int LeavesLevel(TreeNode root, IList<IList<int>> result)
    {
        if(root==null)
        {
            return -;
        }
        int leftLevel = LeavesLevel(root.left, result);
        int rightLevel = LeavesLevel(root.right, result);
        int level = Math.Max(leftLevel, rightLevel)+;
        if(result.Count()<level+)
        {
            result.Add(new List<int>());
        }
        result[level].Add(root.val);
        return level;
    }
}