Sum of Left Leaves

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: Using Recursion

To check if the leaf node is a left left, we can pass bool as param in the function to check if it is a left or right node.

int sumOfLeftLeavesUtil(TreeNode* root, bool isLeft) {
    if (!root) return 0;        
    if (!root->left && !root->right && isLeft) return root->val;
    return sumOfLeftLeavesUtil(root->left, true) + sumOfLeftLeavesUtil(root->right, false);
}

int sumOfLeftLeaves(TreeNode* root) {        
    return sumOfLeftLeavesUtil(root, false);
}