題目出處：https://leetcode.com/problems/longest-common-prefix/

題目描述：

編寫一個函式來查詢字串陣列中最長的公共字首字串。

如果沒有公共字首，則返回空字串“”。

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.

程式碼：

/**
     * @param {string[]} strs array
     * @return {string}
     */
    var longestCommonPrefix = function(strs) {
        var result = [];
        var jiequshuzi;
        //將每一個元素從首字母開始遍歷後的結果拼接
        strs.reduce(function (pre, cur) {
            // console.log(cur);
            for (var i in cur){
                if (pre[i] == cur[i]){
                    result.push(pre[i])
                }else {
                    break
                }
            }
            // console.log(result);
            return result
        });

        //最後一個首字母的下標之後的值，就是結果
        result = result.join('');
        console.log(result);

        //獲取最後一個首字母的下標
        jiequshuzi = result.lastIndexOf(result[0]);

        //檢視結果
        console.log(result.substring(jiequshuzi));
        return result.substring(jiequshuzi)
    };


    var ary = ["flower","flow","flight","fluw"];
    var ary1 = ["teacher","tea","tektic","tecnology"];
    var ary2 = ["dog","racecer","car"];
    longestCommonPrefix(ary)    //fl
    longestCommonPrefix(ary1)   //te
    longestCommonPrefix(ary2)   //
 

但是：

leetcode的檢測結果沒過，報錯資訊：reduce函式需要一個初始值。

看了solution之後修改:

var longestCommonPrefix = function (strs) {
        if (strs.length == 0) return "";
        var prefix = strs[0];
        for (var i = 1; i<strs.length; i++) {
            while (strs[i].indexOf(prefix) != 0) {
                prefix = prefix.substring(0, prefix.length - 1);
                if (prefix.length == 0) return "";
            }
        }
        return prefix
    };
 

筆記:

1.splice方法用於陣列，substring,substr方法用於字串，後2者的區別在於第二個引數，一個表示擷取長度，一個表示擷取結束位置。

2.reduce這個方法的初始值那個引數應該是可選的，是可以的不寫的（reduce相關，進去第3條）