function longestCommonPrefix(strs: string[]): string {
    if (strs.length === 0) return ''
    if (strs.length === 1) return strs[0]
    
    let prefix = ''
    let cnt = 0
    while ( strs.every(str => str.startsWith(prefix)) ) {
        cnt += 1
        if (strs[0].length < cnt) break
        prefix = strs[0].slice(0, cnt)
    }
    if (cnt-1 === 0) return ''
    return strs[0].slice(0, cnt-1)
};