Binary Tree Sum of all left leaves.

iven the root of a binary tree, return the sum of all left leaves.

A leaf is a node with no children. A left leaf is a leaf that is the left child of another node.

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Solution

/**
 * 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 {
   public int SumOfLeftLeaves(TreeNode root)
    {
        return DFS(root,false);
    }
    public int DFS(TreeNode root, bool isLeaf)
    {
        if (root == null)
            return 0;

        if (root.left == null && root.right == null)
        {
            return isLeaf ? root.val : 0;
        }
        return DFS(root.left, true) + DFS(root.right, false);

    }
}