LeetCode in Kotlin

3695. Maximize Alternating Sum Using Swaps

Hard

You are given an integer array nums.

You want to maximize the alternating sum of nums, which is defined as the value obtained by adding elements at even indices and subtracting elements at odd indices. That is, nums[0] - nums[1] + nums[2] - nums[3]...

You are also given a 2D integer array swaps where swaps[i] = [pi, qi]. For each pair [pi, qi] in swaps, you are allowed to swap the elements at indices pi and qi. These swaps can be performed any number of times and in any order.

Return the maximum possible alternating sum of nums.

Example 1:

Input: nums = [1,2,3], swaps = [[0,2],[1,2]]

Output: 4

Explanation:

The maximum alternating sum is achieved when nums is [2, 1, 3] or [3, 1, 2]. As an example, you can obtain nums = [2, 1, 3] as follows.

• Swap nums[0] and nums[2]. nums is now [3, 2, 1].
• Swap nums[1] and nums[2]. nums is now [3, 1, 2].
• Swap nums[0] and nums[2]. nums is now [2, 1, 3].

Example 2:

Input: nums = [1,2,3], swaps = [[1,2]]

Output: 2

Explanation:

The maximum alternating sum is achieved by not performing any swaps.

Example 3:

Input: nums = [1,1000000000,1,1000000000,1,1000000000], swaps = []

Output: -2999999997

Explanation:

Since we cannot perform any swaps, the maximum alternating sum is achieved by not performing any swaps.

Constraints:

• 2 <= nums.length <= 105
• 1 <= nums[i] <= 109
• 0 <= swaps.length <= 105
• swaps[i] = [pi, qi]
• 0 <= pi < qi <= nums.length - 1
• [pi, qi] != [pj, qj]

Solution

class Solution {
    private lateinit var root: IntArray

    fun maxAlternatingSum(nums: IntArray, swaps: Array<IntArray>): Long {
        val n = nums.size
        root = IntArray(n) { it }
        val list = Array(n) { ArrayList<Int>() }
        val oddCount = IntArray(n)
        for (s in swaps) {
            union(s[0], s[1])
        }
        for (i in nums.indices) {
            val r = findRoot(i)
            list[r].add(nums[i])
            if (i % 2 == 1) {
                oddCount[r]++
            }
        }

        var result = 0L
        for (i in 0 until n) {
            if (root[i] != i) {
                continue
            }
            val currentList = list[i]
            val currentOddCount = oddCount[i]
            currentList.sort()
            for (j in currentList.indices) {
                val value = currentList[j].toLong()
                val multiplier = if (j < currentOddCount) -1 else 1
                result += value * multiplier
            }
        }
        return result
    }

    private fun union(a: Int, b: Int) {
        val rootA = findRoot(a)
        val rootB = findRoot(b)
        if (rootA != rootB) {
            if (rootA < rootB) {
                root[rootB] = rootA
            } else {
                root[rootA] = rootB
            }
        }
    }

    private fun findRoot(a: Int): Int {
        if (a == root[a]) {
            return a
        }
        return findRoot(root[a]).also { root[a] = it }
    }
}

This site is open source. Improve this page.