# 14.Longest Common Prefix <span class="tag" data-diff="easy" />
{%hackmd RN5D4nggQRO8wzNqxuvlNw %}

## 題目
Write a function to find the longest common prefix string amongst an array of strings.

If there is no common prefix, return an empty string "".

**Example 1:**

Input: ["flower","flow","flight"]
Output: "fl"

**Example 2:**

Input: ["dog","racecar","car"]
Output: ""
Explanation: There is no common prefix among the input strings.

**Note:**
All given inputs are in lowercase letters a-z.

## 思路
這題不難，順便拿來試試看javascript ES6的解構賦值(Deconstruct assigment)，由於不知道`strs`裡面會傳來多少筆string，利用解構賦值可以取出第一筆字串存在ref，並把剩餘的字串傳給res，接著loop過ref字串，同時用array中的every函式判斷rest中的每一個字串是否與ref中的字元相同，若相同則記錄到ans中，若否則可以直接回傳ans。取值完之後，要注意若strs式空陣列，則ref會是`undefine`，這時可直接回傳空字串。

let [ref, ...res] = strs,
    ans = "";

if(!ref) return "";

for(let i in ref.split("")){
    if(res.every(x => x[i] == ref[i])) ans += ref[i];
    else return ans;
}

return ans;