404. Sum of Left Leaves

leetcode.com/problems/sum-of-left-leaves/

Sum of Left Leaves - LeetCode

/**
 * 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 {
    int sum = 0;
    public int sumOfLeftLeaves(TreeNode root) {
        if(root != null) traverse(root);
        return sum;
    }
    
    public boolean traverse(TreeNode root) {
        if(root.left != null) {
            boolean isLeaf = traverse(root.left);
            if(isLeaf) sum += root.left.val;
        }
        if(root.right != null) {
            traverse(root.right);
        }
        return root.left == null && root.right == null;
    }
}