Leetcode 303. Range Sum Query - Immutabled

class NumArray {
public:
NumArray(vector<int> &nums) {
num = nums;

}

int sumRange(int i, int j) {
int sum = 0;
for (int x = i;x<j+1;x++)
{
sum = sum +num[x];
}
return sum;
}

private:

vector <int> num;
};

class NumArray {
public:
NumArray(vector<int> &nums) {
if (nums.size()>0)
{
sum = new int[nums.size()];
sum[0] = nums[0];
for (int i = 1;i<nums.size();i++)
{
sum[i] = sum[i-1]+nums[i];
}
}

}

int sumRange(int i, int j) {

if (i!=0)
{
return sum[j]-sum[i-1];
}
else
{
return sum[j];
}

}

private:

int *sum;
};