int sumOfLeftLeavesHelper(TreeNode* root, bool is_left) { if (!root) return 0; if (!root->left && !root->right && is_left) return root->val; return sumOfLeftLeavesHelper(root->left, true) + sumOfLeftLeavesHelper(root->right, false); }
int sumOfLeftLeavesHelper(TreeNode* root, bool is_left) { if (!root) { return 0; } if (!root->left && !root->right) { return is_left ? root->val : 0; } return sumOfLeftLeavesHelper(root->left, true) + sumOfLeftLeavesHelper(root->right, false); }
int sumOfLeftLeaves(TreeNode* root) { return sumOfLeftLeavesHelper(root, false); }