How to find the Index of Last Occurrence of Substring in Swift

How to find the Index of Last Occurrence of Substring in Swift ?

Answer

To find the index of the last occurrence of a substring in Swift, you can use the range(of:options:) method of the String class with the .backwards option. This method allows you to search for the substring starting from the end of the string.

✐ Examples

1 Finding the last occurrence index of "l" in "Hello World"

In this example,

We create a string named str with a value of "Hello World".
Next, we define a substring substring with a value of "l" that we want to find the last occurrence of in the main string.
We use the range(of:options:) method of the string str to find the range of the last occurrence of the substring. We specify the .backwards option to search from the end of the string. This method returns an optional range, so we use optional binding (if let) to safely unwrap the result.
If the substring is found, the range constant will hold the range of the substring within the main string. We then calculate the starting index of this range by converting the range's lower bound to an integer offset from the string's start index using the distance(from:to:) method.
Finally, we print the starting index of the last occurrence of the substring within the main string.
If the substring is not found, we print a message indicating that the substring was not found.

Swift Program

import Foundation

let str = "Hello World"
let substring = "l"
if let range = str.range(of: substring, options: .backwards) {
    let index = str.distance(from: str.startIndex, to: range.lowerBound)
    print("The starting index of the last occurrence of \"\(substring)\" is: \(index)")
} else {
    print("Substring \"\(substring)\" not found")
}

Output

The starting index of the last occurrence of "l" is: 9

2 Finding the last occurrence index of "mm" in "Programming Programming"

In this example,

We create a string named str with a value of "Programming Programming".
Next, we define a substring substring with a value of "mm" that we want to find the last occurrence of in the main string.
We use the range(of:options:) method of the string str to find the range of the last occurrence of the substring. We specify the .backwards option to search from the end of the string. This method returns an optional range, so we use optional binding (if let) to safely unwrap the result.
If the substring is found, the range constant will hold the range of the substring within the main string. We then calculate the starting index of this range by converting the range's lower bound to an integer offset from the string's start index using the distance(from:to:) method.
Finally, we print the starting index of the last occurrence of the substring within the main string.
If the substring is not found, we print a message indicating that the substring was not found.

Swift Program

import Foundation

let str = "Programming Programming"
let substring = "mm"
if let range = str.range(of: substring, options: .backwards) {
    let index = str.distance(from: str.startIndex, to: range.lowerBound)
    print("The starting index of the last occurrence of \"\(substring)\" is: \(index)")
} else {
    print("Substring \"\(substring)\" not found")
}

Output

The starting index of the last occurrence of "mm" is: 18

Summary

In this tutorial, we learned How to find the Index of Last Occurrence of Substring in Swift language with well detailed examples.

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How to find the Index of Last Occurrence of Substring in Swift

How to find the Index of Last Occurrence of Substring in Swift ?

Answer

✐ Examples

1 Finding the last occurrence index of "l" in "Hello World"

Swift Program

Output

2 Finding the last occurrence index of "mm" in "Programming Programming"

Swift Program

Output

Summary

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