从字符串数组中查找最常见的子字符串

Question

I want to search a word from an array of strings.

array = ["ram","gopal","varma","govind","ravan","alan"]

if my search text is goal i want to list as follows:

result = ["gopal","govind","alan"]

ie in gopal & goal only p is missing so it should be in search list with higher priority.

Is there any way to do such filtering?

Answer 1

You want to find longest common subsequences. I would suggest you to look at this excelent article on Ray Wenderlich's Swift Algorithm Club where you can find your solution with examples.

EDIT:

Then you have to iterate over your array and keep track of how long a subsequence is for each world (for example in dictionary). Then you have to sort your array by the subsequences lengths.

For example like this:

let array = ["ram", "gopal", "varma", "govind", "ravan", "alan"]
let searchTerm = "goal"

var dictionary: [String: Int] = [:]
for element in array {
    dictionary[element] = searchTerm.longestCommonSubsequence(element).count
}

let result = dictionary.sorted(by: { $0.1 > $1.1 }).map { $0.key }

Answer 2

The longest common subsequence between two strings can be defined recursively as follows :

func lcs(_ str1: String, _ str2: String, _ i: String.Index, _ j: String.Index) -> Int 
{
    if (i == str1.startIndex || j == str2.startIndex) {
        return 0
    }

    let beforeI = str1.index(before: i)
    let beforeJ = str2.index(before: j)

    if str1[beforeI] == str2[beforeJ] {
        return 1 + lcs(str1, str2, beforeI, beforeJ)
    } else {
        return max(lcs(str1, str2, i, beforeJ), lcs(str1, str2, beforeI, j))
    }
}

You can find a complete explanation of how this dynamic programming algorithm works here .

So, given an array of strings and a search text :

let array = ["ram", "gopal", "varma", "govind", "ravan", "alan", "logan"]
let searchText = "goal"

We can associate a score to each element of the array, filter only those that have a non-zero score, sort them by score, and then only key the words from the tuples :

let result = array
    .map { ($0, lcs(searchText,
                    $0,
                    searchText.endIndex,
                    $0.endIndex)) }
    .filter { $0.1 > 0 }
    .sorted { $0.1 > $1.1 }
    .map { $0.0 }

print(result)

Which yields :

["gopal", "govind", "alan", "logan", "ram", "varma", "ravan"]