404. 左叶子之和

题目链接

/**
 * @param {TreeNode} root
 * @return {number}
 */
var sumOfLeftLeaves = function(root) {
    if (root === null) return 0;
    let leftVal = 0;
    if (root.left && !root.left.left && !root.left.right) {
        leftVal = root.left.val;
    } else {
        leftVal = sumOfLeftLeaves(root.left);
    }
    return leftVal + sumOfLeftLeaves(root.right);
};