[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

动态规划

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

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

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