1239-maximum-length-of-a-concatenated-string-with-unique-characters.js

/**
 * @param {string[]} arr
 * @return {number}
 */
const maxLength = function(arr) {
    let maxLen = 0;
    arr = arr.filter(isUnique);
    const mem = {};
    maxLen = dfs(arr, "", 0, maxLen, mem);
    
    return maxLen;
};

function dfs(arr, path, i, maxLen, mem) {
    if (mem[path]) return mem[path];
    let pathIsUnique = isUnique(path);
    if (pathIsUnique) {
        maxLen = Math.max(path.length, maxLen);
    } 
    if (i === arr.length || !pathIsUnique) {
        mem[path] = maxLen;
        return maxLen;
    }
    for (let j = i; j < arr.length; j++) {
        maxLen = dfs(arr, path + arr[j], j + 1, maxLen, mem);
    }


    mem[path] = maxLen;
    return maxLen;
}

function isUnique(str) {
    const map = {}
    for (let i = 0; i < str.length; i++) {
        if (map[str[i]]) return false;
        map[str[i]] = 1;
    }
    
    return true;
}