leetcode记录：难度简单：14. 最长相同字首

题目出处：https://leetcode.com/problems/longest-common-prefix/

题目描述：

编写一个函数来查找字符串数组中最长的公共前缀字符串。

如果没有公共前缀，则返回空字符串“”。

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.

代码：

/**
     * @param {string[]} strs array
     * @return {string}
     */
    var longestCommonPrefix = function(strs) {
        var result = [];
        var jiequshuzi;
        //将每一个元素从首字母开始遍历后的结果拼接
        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
        });

        //最后一个首字母的下标之后的值，就是结果
        result = result.join('');
        console.log(result);

        //获取最后一个首字母的下标
        jiequshuzi = result.lastIndexOf(result[0]);

        //查看结果
        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的检测结果没过，报错信息：reduce函数需要一个初始值。

看了solution之后修改:

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
    };

笔记:

1.splice方法用于数组，substring,substr方法用于字符串，后2者的区别在于第二个参数，一个表示截取长度，一个表示截取结束位置。

2.reduce这个方法的初始值那个参数应该是可选的，是可以的不写的（reduce相关，进去第3条）