Convert To Hex

Given an integer num, return a string representing its hexadecimal representation. For negative integers, two’s complement method is used. All the letters in the answer string should be lowercase characters, and there should not be any leading zeros in the answer except for the zero itself. Source – solution

package questions

import _utils.UseCommentAsDocumentation
import utils.shouldBe

/**
 * Given an integer num, return a string representing its hexadecimal representation.
 * For negative integers, two’s complement method is used.
 * All the letters in the answer string should be lowercase characters,
 * and there should not be any leading zeros in the answer except for the zero itself.
 * [Source](https://leetcode.com/problems/convert-a-number-to-hexadecimal/) – [solution](https://leetcode.com/problems/convert-a-number-to-hexadecimal/discuss/824192/Java-100-Time-with-Detailed-Explanation)
 */
@UseCommentAsDocumentation
private fun toHex(num: Int): String {
    if (num in 0..9) {
        return "$num"
    }
    val hexMap = mapOf<Int, Char>(
        10 to 'a',
        11 to 'b',
        12 to 'c',
        13 to 'd',
        14 to 'e',
        15 to 'f'
    )
    var temp = num

    var result = ""
    for (i in 1..8) {
        if (temp == 0) {
            break
        }
        val last4bits = temp.and(0b1111)
        if (last4bits <= 9) {
            result = last4bits.toString() + result
        } else {
            result = hexMap[last4bits].toString() + result
        }
        temp = temp.shr(4)
    }
    return result
}

fun main() {
    toHex(26) shouldBe "1a"
    toHex(27) shouldBe "1b"
    toHex(10) shouldBe "a"
    toHex(1) shouldBe "1"
    toHex(-1) shouldBe "ffffffff"
}

---

View on GitHub

Updated on 2021-11-04