LeetCode Sum of Left Leaves

1. Title

2. Ideas (description in Java language)

Determine whether the current node is the left node, if it is, add the value of the node, and then recurse the left and right subtrees

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    
    
    public int sumOfLeftLeaves(TreeNode root) {
    
    
        if(root == null){
    
    
            return 0;
        }
        int cnt = 0;
        if(root.left!=null && root.left.left == null && root.left.right==null){
    
    
            cnt+=root.left.val;
        }
        cnt+=sumOfLeftLeaves(root.left);
        cnt+=sumOfLeftLeaves(root.right);
        return cnt;
    }
}