LeetCode Q303: Range Sum Query - Immutable

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.

Solution:

	class NumArray {
	public:
	NumArray(vector<int> &nums) {
	if(nums.empty())
	return;
	sums.resize(nums.size()+1);
	for(int i=1; i<sums.size(); i++){
	sums[i] = sums[i-1]+nums[i-1];
	}
	}
	int sumRange(int i, int j) {
	return sums[j+1]-sums[i];
	}
	vector<int> sums;
	};
	// Your NumArray object will be instantiated and called as such:
	// NumArray numArray(nums);
	// numArray.sumRange(0, 1);
	// numArray.sumRange(1, 2);

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