307. 区域和检索 - 数组可修改

class NumArray 
{
    vector<int> num;
public:
    NumArray(vector<int>& nums) 
    {
        num = nums;
    }
    
    void update(int i, int val) 
    {
        num[i] = val;
    }
    
    int sumRange(int i, int j) 
    {
        int sum = 0;
        for(int k = i;k <= j;k ++) sum += num[k];
        return sum;
    }
};