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Rooted by: Searching substring inside another string
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  • Algorithms
    Logic
    Search
    Strings
    Data Types
    Code 
    fun findFirstSubString(string: String, subString: String): Int? =
    if (subString.isEmpty()) null 
    else subString.toRegex().find(string)?.range?.first
     Test Cases 
    import org.junit.Assert
import org.junit.Test

class SimpleSubStringSearchKtTest {

    @Test
    fun `Substring longer than string`() {
        Assert.assertNull(findFirstSubString("12345", "123456"))
        Assert.assertNull(findFirstSubString("54321", "123456"))
    }

    @Test
    fun `Empty string`() {
        Assert.assertNull(findFirstSubString("", "123456"))
    }

    @Test
    fun `Empty substring`() {
        Assert.assertNull(findFirstSubString("12323123", ""))
    }

    @Test
    fun `Empty substring and string`() {
        Assert.assertNull(findFirstSubString("", ""))
    }

    @Test
    fun `Correct finding`() {
        Assert.assertEquals(findFirstSubString("12345", "123"), 0)
        Assert.assertEquals(findFirstSubString("54321321", "321"), 2)
        Assert.assertEquals(findFirstSubString("123456789ABCDE123456789", "ABCDE"), 9)
        Assert.assertEquals(findFirstSubString("123456789ABCDE123456789", "A"), 9)
        Assert.assertEquals(findFirstSubString("123456789ABCDE123456789", "a"), null)
        Assert.assertEquals(findFirstSubString("111234", "1234"), 2)
    }
}
    View Run Output
  • Code
    • fun findFirstSubString(string: String, subString: String): Int? {
    • val stringArray = string.toList()
    • val substringArray = subString.toList()
    • if (stringArray.size < substringArray.size || stringArray.isEmpty() || substringArray.isEmpty()) {
    • return null
    • }
    • var counter = 0
    • var startIndex = 0
    • var i = 0
    • while (i < stringArray.size) {
    • if (stringArray[i] == substringArray[counter]) {
    • if(counter == 0) {
    • startIndex = i
    • }
    • if ((counter + 1) == substringArray.size) {
    • return startIndex
    • }
    • counter++
    • i++
    • }
    • else {
    • if (counter > 0) {
    • i = startIndex + 1
    • }
    • else {
    • i++
    • }
    • counter = 0
    • startIndex = 0
    • }
    • println(i)
    • }
    • return null
    • }
    • fun findFirstSubString(string: String, subString: String): Int? =
    • if (subString.isEmpty()) null
    • else subString.toRegex().find(string)?.range?.first