Set Mismatch

You have a set of integers s, which originally contains all the numbers from 1 to n. Unfortunately, due to some error, one of the numbers in s got duplicated to another number in the set, which results in repetition of one number and loss of another number. Find the number that occurs twice and the number that is missing and return them in the form of an array. Source

package questions

import _utils.UseCommentAsDocumentation
import utils.shouldBe

/**
 * You have a set of integers s, which originally contains all the numbers from 1 to n.
 * Unfortunately, due to some error, one of the numbers in s got duplicated to another number in the set,
 * which results in repetition of one number and loss of another number.
 * Find the number that occurs twice and the number that is missing and return them in the form of an array.
 * [Source](https://leetcode.com/problems/set-mismatch/)
 */
@UseCommentAsDocumentation
private fun findErrorNums(nums: IntArray): IntArray {
    val result = IntArray(2) { -1 }
    val seen = HashSet<Int>(nums.size)
    val possibleMissing = mutableSetOf<Int>()
    var trueIndex = 0
    nums.sorted().forEach { i -> // GOTCHA: you've sorted the array, so you can't use forEachIndexed
        if (trueIndex + 1 != i) {  // out of index so potentially missing
            possibleMissing.add(trueIndex + 1) // index is the missing element
        }
        if (seen.contains(i)) { // seen check
            result[0] = i
        }
        trueIndex++
        seen.add(i)
    }
    possibleMissing.forEach { // find which element is missing
        if (!seen.contains(it)) {
            result[1] = it
            return result // missing element found return the result
        }
    }
    result[1] = nums.size // no missing element found
    return result
}

fun main() {
    // 2,3,3,4,5,6
    findErrorNums(nums = intArrayOf(3, 2, 3, 4, 6, 5)) shouldBe intArrayOf(3, 1)
    findErrorNums(nums = intArrayOf(1, 5, 3, 2, 2, 7, 6, 4, 8, 9)) shouldBe intArrayOf(2, 10)
    findErrorNums(nums = intArrayOf(3, 2, 2)) shouldBe intArrayOf(2, 1)
    findErrorNums(nums = intArrayOf(1, 2, 2, 4)) shouldBe intArrayOf(2, 3)
    findErrorNums(nums = intArrayOf(1, 2, 3, 4, 5, 6, 7, 7, 9)) shouldBe intArrayOf(7, 8)
}

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Updated on 2021-11-02