404. Sum of Left Leaves - cocoder39/coco39_LC GitHub Wiki

int sumOfLeftLeaves(TreeNode* root) {
        int res = 0;
        if (! root) return res;
        
        queue<TreeNode*> q;
        q.push(root);
        while (! q.empty()) {
            int sz = q.size();
            for (int i = 0; i < sz; i++) {
                TreeNode* node = q.front();
                q.pop();
                if (node->left) {
                    if (isLeave(node->left)) {
                        res += node->left->val;
                    } else { //unnecessary to push a leave into queue
                        q.push(node->left);
                    }
                }
                if (node->right) {
                    if (! isLeave(node->right)) {
                        q.push(node->right);
                    }
                }
            }
        }
        return res;
    }

int sumOfLeftLeaves(TreeNode* root) {
        if (! root) {
            return 0;
        } else if (root->left && ! root->left->left && ! root->left->right) {
            return root->left->val + sumOfLeftLeaves(root->right);
        } else {
            return sumOfLeftLeaves(root->left) + sumOfLeftLeaves(root->right);
        }
    }