Leetcode: 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:

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

比较简单。

class NumArray {
public:
NumArray(vector<int> &nums) {
m_numsSum.resize(nums.size());
for (int i = 0; i < nums.size(); ++i) {
m_numsSum[i] = (i == 0 ? nums[i] : m_numsSum[i-1] + nums[i]);
}
}

int sumRange(int i, int j) {
return (i == 0 ? m_numsSum[j] : m_numsSum[j] - m_numsSum[i-1]);
}

private:
vector<int> m_numsSum;
};

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