export function longestCommonPrefix(words: string[]): string {
  let ref = ""
  for(let i=0;i<words.length;i++){
    if(i==0){
      ref = words[i]
    }else{
      let pre_ref = ""
      for(let j in words[i]){
          if(j<ref.length && ref[j]==words[i][j]){
            pre_ref+=words[i][j]
          }else{
            return pre_ref
          }
      }
      ref = pre_ref
    }
  }

  return ref
}