[LeetCode] 404. Sum of Left Leaves

Problem

Find the sum of all left leaves in a given binary tree.

Example:

    3
   / \
  9  20
    /  \
   15   7

There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.

Solution - Recursive

class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        if (root == null) return 0;
        int res = 0;
        if (root.left != null) {
            if (root.left.left == null && root.left.right == null) res += root.left.val;
            else res += sumOfLeftLeaves(root.left);
        }
        res += sumOfLeftLeaves(root.right);
        return res;
    }
}

Solution - Iterative

class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        if (root == null) return 0;
        int res = 0;
        Deque<TreeNode> stack = new ArrayDeque<>();
        stack.push(root);
        while (!stack.isEmpty()) {
            TreeNode cur = stack.pop();
            if (cur.left != null) {
                if (cur.left.left == null && cur.left.right == null) {
                    res += cur.left.val;
                } else {
                    stack.push(cur.left);
                }
            }
            if (cur.right != null) {
                if (cur.right.left != null || cur.right.right != null) {
                    stack.push(cur.right);
                }
            }
        }
        return res;
    }
}