303. Range Sum Query - Immutable

• Difficulty: Easy

• Topics: Dynamic Programming

• Similar Questions:

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  • Range Sum Query - Mutable

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Problem:

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:

Solutions:

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

    int sumRange(int i, int j) {
        if (i == 0) return prefixSum[j];
        return prefixSum[j] - prefixSum[i - 1];
    }

private:
    vector<int> prefixSum;

};

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