K-Similar Strings

Problem statement

Strings s1 and s2 are k-similar (for some non-negative integer k) if we can swap the positions of two letters in s1 exactly k times so that the resulting string equals s2.

Given two anagrams s1 and s2, return the smallest k for which s1 and s2 are k-similar.

Example 1:

Input: s1 = "ab", s2 = "ba"Output: 1

Example 2:

Input: s1 = "abc", s2 = "bca"Output: 2

Constraints:

• 1 <= s1.length <= 20
• s2.length == s1.length
• s1 and s2 contain only lowercase letters from the set {'a', 'b', 'c', 'd', 'e', 'f'}.
• s2 is an anagram of s1.

My solution

/**
 * @param {string} s1
 * @param {string} s2
 * @return {number}
 */
var kSimilarity = function(s1, s2) {
    if (s1 === s2) {
        return 0
    }
    
    const queue = [s1]
    const visited = new Set([s1])
    let steps = 0;
    
    
    while (queue.length) {
        const size = queue.length;
        
        for (let i = 0; i < size; i++) {
            const currStr = queue.shift();
            
            if (currStr === s2) {
                return steps;
            }
            
            const nextStrs = getNextStr(currStr, s2)
            for (const next of nextStrs) {
                if (!visited.has(next)) {
                    visited.add(next);
                    queue.push(next)
                }
            }
        }
        
        steps++
    }
    return steps
};

function getNextStr(s1, s2) {
    const nextStrs = [];
    let i = 0;
    
    while (i < s1.length) {
        if (s1.charAt(i) !== s2.charAt(i)) {
            break;
        }
        i++;
    }
    
    for (let j = i + 1; j < s1.length; j++) {
        if (s1.charAt(j) === s2.charAt(i)) {
            nextStrs.push(swap(s1, i, j))
        }
    }
    return nextStrs
}

function swap(str, i, j) {
    let arr = str.split("");
    let temp = arr[i];
    arr[i] = arr[j];
    arr[j] = temp;
    return arr.join("");
}