g0301_0400.s0307_range_sum_query_mutable.NumArray Maven / Gradle / Ivy

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package g0301_0400.s0307_range_sum_query_mutable;

// #Medium #Array #Design #Segment_Tree #Binary_Indexed_Tree
// #2022_07_07_Time_99_ms_(88.96%)_Space_138.9_MB_(5.17%)

/**
 * 307 - Range Sum Query - Mutable\.
 *
 * Medium
 *
 * Given an integer array `nums`, handle multiple queries of the following types:
 *
 * 1.  **Update** the value of an element in `nums`.
 * 2.  Calculate the **sum** of the elements of `nums` between indices `left` and `right` **inclusive** where `left <= right`.
 *
 * Implement the `NumArray` class:
 *
 * *   `NumArray(int[] nums)` Initializes the object with the integer array `nums`.
 * *   `void update(int index, int val)` **Updates** the value of `nums[index]` to be `val`.
 * *   `int sumRange(int left, int right)` Returns the **sum** of the elements of `nums` between indices `left` and `right` **inclusive** (i.e. `nums[left] + nums[left + 1] + ... + nums[right]`).
 *
 * **Example 1:**
 *
 * **Input**
 *
 *     ["NumArray", "sumRange", "update", "sumRange"]
 *     [[[1, 3, 5]], [0, 2], [1, 2], [0, 2]]
 *
 * **Output:** [null, 9, null, 8]
 *
 * **Explanation:**
 *
 *     NumArray numArray = new NumArray([1, 3, 5]);
 *     numArray.sumRange(0, 2); // return 1 + 3 + 5 = 9
 *     numArray.update(1, 2); // nums = [1, 2, 5]
 *     numArray.sumRange(0, 2); // return 1 + 2 + 5 = 8 
 *
 * **Constraints:**
 *
 * *   1 <= nums.length <= 3 * 10⁴
 * *   `-100 <= nums[i] <= 100`
 * *   `0 <= index < nums.length`
 * *   `-100 <= val <= 100`
 * *   `0 <= left <= right < nums.length`
 * *   At most 3 * 10⁴ calls will be made to `update` and `sumRange`.
**/
public class NumArray {
    private int[] nums;
    private int sum;

    public NumArray(int[] nums) {
        this.nums = nums;
        sum = 0;
        for (int num : nums) {
            sum += num;
        }
    }

    public void update(int index, int val) {
        sum -= nums[index] - val;
        nums[index] = val;
    }

    public int sumRange(int left, int right) {
        int sumRange = 0;
        if ((right - left) < nums.length / 2) {
            // Array to sum is less than half
            for (int i = left; i <= right; i++) {
                sumRange += nums[i];
            }
        } else {
            // Array to sum is more than half
            // Better to take total sum and substract the numbers not in range
            sumRange = sum;
            for (int i = 0; i < left; i++) {
                sumRange -= nums[i];
            }
            for (int i = right + 1; i < nums.length; i++) {
                sumRange -= nums[i];
            }
        }
        return sumRange;
    }
}