LeetCode 303. Range Sum Query - Immutable

题目

求区间，固定的数组，用前缀和数组

class NumArray {
public:
    vector<int> prefix;
    NumArray(vector<int>& nums) {
        prefix.push_back(0);
        for(int i=0;i<nums.size();i++)
        {
            prefix.push_back(prefix[i]+nums[i]);
        }
    }
    
    int sumRange(int i, int j) {
        
        return prefix[j+1]-prefix[i];
    }
};

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