// @Title: 左叶子之和 (Sum of Left Leaves)
// @Author: qisiii
// @Date: 2024-09-15 16:56:33
// @Runtime: 0 ms
// @Memory: 40.2 MB
// @comment: 
// @flag: 
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        return leftSum(root);
    }
    private int leftSum(TreeNode root){
        if(root==null){
            return 0;
        }
        int sum=0;
        if(root.left!=null&&root.left.left==null&&root.left.right==null){
           sum+=root.left.val;
        }
        return sum+leftSum(root.left)+leftSum(root.right);
    }
}