void output(int lower, int upper, vector<string>& result) {

if(upper == lower) {

result.push_back(to_string(lower));

} else {

result.push_back(to_string(lower) + "->" + to_string(upper));

}

}

vector<string> findMissingRanges(vector<int>& nums, int lower, int upper) {

vector<string> result;

// case: array empty, both lower and upper inclusive

if(nums.empty()) {

output(lower, upper, result);

return result;

}

// case: lower inclusive

if(nums[0] - lower > 0) {

output(lower, nums[0] - 1, result);

}

for(int i = 1; i < nums.size(); ++i) {

if(nums[i] - nums[i - 1] > 1) {

output(nums[i - 1] + 1, nums[i] - 1, result);

}

}

// case: upper inclusive

if(upper - nums[nums.size() - 1] > 0) {

output(nums[nums.size() - 1] + 1, upper, result);

}

return result;

}