String Compression II.js

var getLengthOfOptimalCompression = function(s, k) {
    const memo = new Map()
    
    const backtrack = (i, lastChar, lastCharCount, k) => {
        if (k < 0) return Number.POSITIVE_INFINITY
        if (i >= s.length) return 0
        
        const memoKey = `${i}#${lastChar}#${lastCharCount}#${k}`
        if (memoKey in memo) return memo[memoKey]
        
        if (s[i] === lastChar) {
            const incrementor = [1, 9, 99].includes(lastCharCount) ? 1 : 0
            memo[memoKey] = incrementor + backtrack(i+1, lastChar, lastCharCount+1, k)
        } else {
            memo[memoKey] = Math.min(
                1 + backtrack(i+1, s[i], 1, k), //keep char
                backtrack(i+1, lastChar, lastCharCount, k-1) //delete char
            )
        }
        return memo[memoKey]
    }
    return backtrack(0, '', 0, k)
};