sum-of-left-leaves.java

// Given 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.
//
//  
// Example 1:
//
//
// Input: root = [3,9,20,null,null,15,7]
// Output: 24
// Explanation: There are two left leaves in the binary tree, with values 9 and 15 respectively.
//
//
// Example 2:
//
//
// Input: root = [1]
// Output: 0
//
//
//  
// Constraints:
//
//
// 	The number of nodes in the tree is in the range [1, 1000].
// 	-1000 <= Node.val <= 1000
//
//


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