# 307. Range Sum Query - Mutable

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

The update(i, val) function modifies nums by updating the element at index i to val.

Example:

Given nums = \[1, 3, 5]

sumRange(0, 2) -> 9 update(1, 2) sumRange(0, 2) -> 8

Note:

The array is only modifiable by the update function. You may assume the number of calls to update and sumRange function is distributed evenly.

## Solution <a href="#solution" id="solution"></a>

```java
public class NumArray {

      int[] nums;
    int[] BIT;
    int n;


    public NumArray(int[] nums) {
        this.nums = nums;
        n = nums.length;
        BIT = new int[n + 1];
        for (int i = 0; i < nums.length; i++) {
            init(i, nums[i]);
        }
    }

    private void init(int i, int val) {
        i++;
        while (i <= n) {
            BIT[i] += val;
            i += (i & -i);
        }
    }

    void update(int i, int val) {
        int diff = val - nums[i];
        nums[i] = val;
        init(i, diff);
    }

    private int sum(int i) {
        i++;
        int sum = 0;
        while (i > 0) {
            sum += BIT[i];
            i -= (i & -i);
        }
        return sum;
    }

    public int sumRange(int i, int j) {
        return sum(j) - sum(i - 1);
    }
}


// Your NumArray object will be instantiated and called as such:
// NumArray numArray = new NumArray(nums);
// numArray.sumRange(0, 1);
// numArray.update(1, 10);
// numArray.sumRange(1, 2);
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://anand-aryan.gitbook.io/leetcode/307.-range-sum-query-mutable.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.