Summary Ranges

You are given a sorted unique integer array nums.

Return the smallest sorted list of ranges that cover all the numbers in the array exactly. That is, each element of nums is covered by exactly one of the ranges, and there is no integer x such that x is in one of the ranges but not in nums.

Each range [a,b] in the list should be output as: *"a->b" if a != b

• "a" if a == b

  Source

package questions

import utils.shouldBe

/**
 * You are given a sorted unique integer array nums.
 *
 * Return the smallest sorted list of ranges that cover all the numbers in the array exactly.
 * That is, each element of nums is covered by exactly one of the ranges,
 * and there is no integer x such that x is in one of the ranges but not in nums.
 *
 * Each range [a,b] in the list should be output as:
 * *"a->b" if a != b
 * * "a" if a == b
 *
 * [Source](https://leetcode.com/problems/summary-ranges/)
 */

private fun summaryRanges(nums: IntArray): List<String> {
    if (nums.isEmpty()) return emptyList()
    if (nums.size == 1) return listOf(nums[0].toString())

    val result = mutableListOf<String>()
    findRange(nums, startIndex = 0, currentIndex = 1, result)
    return result
}

private fun findRange(nums: IntArray, startIndex: Int, currentIndex: Int, result: MutableList<String>) {
    if (currentIndex > nums.lastIndex) { // end
        // add the remaining
        val start = nums[startIndex]
        val end = nums[nums.lastIndex]
        addToList(start, end, result)
        return
    }
    return if (nums[currentIndex - 1] == nums[currentIndex] - 1) { // Check if sequential i.e (prevElem+1 = current)
        findRange(nums, startIndex = startIndex, currentIndex = currentIndex + 1, result)
    } else {
        val start = nums[startIndex]
        val end = nums[currentIndex - 1]
        addToList(start, end, result)
        findRange(
            nums,
            startIndex = currentIndex, // start from current as current element is the one that violated
            currentIndex = currentIndex + 1, // should be 1 step ahead of [startIndex]
            result
        )
    }
}

private fun addToList(start: Int, end: Int, result: MutableList<String>) {
    if (start == end) result.add("$start")
    else result.add("$start->$end")
}

fun main() {
    summaryRanges(nums = intArrayOf(-1)) shouldBe listOf("-1")
    summaryRanges(nums = intArrayOf(0, 1, 2, 4, 5, 7)) shouldBe listOf("0->2", "4->5", "7")
    summaryRanges(nums = intArrayOf(0, 2, 3, 4, 6, 8, 9)) shouldBe listOf("0", "2->4", "6", "8->9")
    summaryRanges(nums = intArrayOf()) shouldBe listOf()
    summaryRanges(nums = intArrayOf(0)) shouldBe listOf("0")
}

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Updated on 2021-10-15