LeetCode:Range Sum Query - Immutable

Range Sum Query - Immutable

Total Accepted: 29091  Total Submissions: 118678  Difficulty: Easy

Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.

Example:

Given nums = [-2, 0, 3, -5, 2, -1]

sumRange(0, 2) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3

Note:

1. You may assume that the array does not change.
2. There are many calls to sumRange function.

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c++ code:

class NumArray {
public:
    NumArray(vector<int> &nums) {
        sums.push_back(0);
        for(int i=0;i<nums.size();i++) {
            sums.push_back(sums.back() + nums[i]);
        }
    }

    int sumRange(int i, int j) {
        return sums[j + 1] - sums[i];
    }
private:
    vector<int> sums;
};


// Your NumArray object will be instantiated and called as such:
// NumArray numArray(nums);
// numArray.sumRange(0, 1);
// numArray.sumRange(1, 2);