LeetCode in Kotlin

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.

Solution

class NumArray(private val nums: IntArray) {
    private var sum = 0

    init {
        for (num in nums) {
            sum += num
        }
    }

    fun update(index: Int, `val`: Int) {
        sum -= nums[index] - `val`
        nums[index] = `val`
    }

    fun sumRange(left: Int, right: Int): Int {
        var sumRange = 0
        if (right - left < nums.size / 2) {
            // Array to sum is less than half
            for (i in left..right) {
                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 (i in 0 until left) {
                sumRange -= nums[i]
            }
            for (i in right + 1 until nums.size) {
                sumRange -= nums[i]
            }
        }
        return sumRange
    }
}

/*
 * Your NumArray object will be instantiated and called as such:
 * var obj = NumArray(nums)
 * obj.update(index,`val`)
 * var param_2 = obj.sumRange(left,right)
 */

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