[LeeCode]14. 最长公共前缀

题目链接:https://leetcode-cn.com/problems/longest-common-prefix/

题目描述:

编写一个函数来查找字符串数组中的最长公共前缀。

如果不存在公共前缀，返回空字符串 ""。

示例:

示例 1:

输入: ["flower","flow","flight"]
输出: "fl"

示例 2:

输入: ["dog","racecar","car"]
输出: ""
解释: 输入不存在公共前缀。

说明:

所有输入只包含小写字母 a-z 。

思路:

思路1:

python特性,取每一个单词的同一位置的字母,看是否相同.

思路2:

取一个单词s,和后面单词比较,看s与每个单词相同的最长前缀是多少!遍历所有单词

思路3:

按字典排序数组,比较第一个,和最后一个单词,有多少前缀相同.

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代码:

python

思路一:

class Solution:
    def longestCommonPrefix(self, strs):
        """
        :type strs: List[str]
        :rtype: str
        """
        res = ""
        for tmp in zip(*strs):
            tmp_set = set(tmp)
            if len(tmp_set) == 1:
                res += tmp[0]
            else:
                break
        return res

思路二:

python

class Solution:
    def longestCommonPrefix(self, s: List[str]) -> str:
        if not s:
            return ""
        res = s[0]
        i = 1
        while i < len(s):
            while s[i].find(res) != 0:
                res = res[0:len(res)-1]
            i += 1
        return res

java

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) return "";
        String res = strs[0];
        int i = 1;
        while (i < strs.length) {
            while (strs[i].indexOf(res) != 0) {
                res = res.substring(0, res.length() - 1);
            }
            i += 1;
        }
        return res;

    }
}

思路三:

python

class Solution:
    def longestCommonPrefix(self, s: List[str]) -> str:
        if not s:
            return ""
        s.sort()
        n = len(s)
        a = s[0]
        b = s[n-1]
        res = ""
        for i in range(len(a)):
            if i < len(b) and a[i] == b[i]:
                res += a[i]
            else:
                break
        return res

java

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) return "";
        StringBuilder res = new StringBuilder();
        Arrays.sort(strs);
        // 字符串转数组
        char[] a = strs[0].toCharArray();
        char[] b = strs[strs.length - 1].toCharArray();
        for (int i = 0; i < a.length; i++) {
            if (i < b.length && a[i] == b[i]) {
                res.append(a[i]);
            }
            else{
                break;
            }
        }
        return res.toString();

    }
}