# [leetcode] Range Sum Query – Immutable

Range Sum Query – Immutable

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

Dynamic programming. Sumleft

```class NumArray {
public:
vector<long> leftSum;
NumArray(vector<int> &nums) {
leftSum = vector<long>(nums.size(), 0);
if(nums.size() == 0) return ;
leftSum[0] = nums[0];
for(int i = 1; i < nums.size(); i++){
leftSum[i] = leftSum[i - 1] + nums[i];
}
}

int sumRange(int i, int j) {
if(i > j || i < 0 || j >= leftSum.size()) return 0;
if(i == 0) return (int)leftSum[j];
else return (int)(leftSum[j] - leftSum[i - 1]);
}
};

// 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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