Range Sum Query - Immutable（C++區域和檢索 - 數組不可變）

解題思路：

（1）先保存數組

（2）再按照下標訪問即可

class NumArray {
public:
    vector<int> v;
    NumArray(vector<int>& nums) {
        v.insert(v.begin(),nums.begin(),nums.end());
    }
    
    int sumRange(int i, int j) {
        int sum = 0;
        for(int k=i;k<=j;k++) sum+=v[k];
        return sum;
    }
};

/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray* obj = new NumArray(nums);
 * int param_1 = obj->sumRange(i,j);
 */