LeetCode in Kotlin

2640. Find the Score of All Prefixes of an Array

Medium

We define the conversion array conver of an array arr as follows:

• conver[i] = arr[i] + max(arr[0..i]) where max(arr[0..i]) is the maximum value of arr[j] over 0 <= j <= i.

We also define the score of an array arr as the sum of the values of the conversion array of arr.

Given a 0-indexed integer array nums of length n, return an array ans of length n where ans[i] is the score of the prefix nums[0..i].

Example 1:

Input: nums = [2,3,7,5,10]

Output: [4,10,24,36,56]

Explanation:

For the prefix [2], the conversion array is [4] hence the score is 4

For the prefix [2, 3], the conversion array is [4, 6] hence the score is 10

For the prefix [2, 3, 7], the conversion array is [4, 6, 14] hence the score is 24

For the prefix [2, 3, 7, 5], the conversion array is [4, 6, 14, 12] hence the score is 36

For the prefix [2, 3, 7, 5, 10], the conversion array is [4, 6, 14, 12, 20] hence the score is 56

Example 2:

Input: nums = [1,1,2,4,8,16]

Output: [2,4,8,16,32,64]

Explanation:

For the prefix [1], the conversion array is [2] hence the score is 2

For the prefix [1, 1], the conversion array is [2, 2] hence the score is 4

For the prefix [1, 1, 2], the conversion array is [2, 2, 4] hence the score is 8

For the prefix [1, 1, 2, 4], the conversion array is [2, 2, 4, 8] hence the score is 16

For the prefix [1, 1, 2, 4, 8], the conversion array is [2, 2, 4, 8, 16] hence the score is 32

For the prefix [1, 1, 2, 4, 8, 16], the conversion array is [2, 2, 4, 8, 16, 32] hence the score is 64

Constraints:

• 1 <= nums.length <= 105
• 1 <= nums[i] <= 109

Solution

class Solution {
    fun findPrefixScore(nums: IntArray): LongArray {
        var max = Integer.MIN_VALUE
        var sum = 0L
        val res = LongArray(nums.size)
        for (i in 0 until nums.size) {
            val curr = nums[i]
            max = maxOf(max, curr)
            sum += max + curr
            res[i] = sum
        }
        return res
    }
}

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