145.PostorderTraversal.cs

// 145. Binary Tree Postorder Traversal
// Given the root of a binary tree, return the postorder traversal of its nodes' values.

// Example 1:
// Input: root = [1,null,2,3]
// Output: [3,2,1]
// Example 2:

// Input: root = []
// Output: []
// Example 3:

// Input: root = [1]
// Output: [1]
// /**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
public class Solution {
    IList<int> result = new List<int>();
    public IList<int> PostorderTraversal(TreeNode root) {
        if(root == null)
            return result;
        PostorderTraversal(root.left);
        PostorderTraversal(root.right);
        result.Add(root.val);
        
        return result;
    }
}