First Recurring Character 

function ReturnReccurringCharacter(str){
    
    // if string is of other data type return invalid datatye
    
    // iterate through each char and then stoe the number of times its been seen
    let seenTable = new Map()
    
    for(let i = 0; i < str.length; i++){
        let key = str[i]
        if(seenTable.get(key) ===  undefined ){
            seenTable.set(key, 1)
        }else{
            seenTable.set(key, seenTable.get(key)+1)
        }
    }
    
    let mostRepeated = ""
    let mostRepeatedValue = ""
    
    for (let [key, value] of seenTable)
    {
        console.log(seenTable)

        if(value >= 2){
            return key
        }
        
    }

    
    // choose most repeated char from the hash table
    return null
}

function RecurringCharacter(input){
    let map = {};
    for(let i = 0; i < input.length; i++){
        if(map[input[i]] != undefined){
            return input[i]
        }else{
            map[input[i]] = 1
        }
    }
    
    return undefined
}

console.log(RecurringCharacter([1,2,2,23,5,5]))