LeetCode刷题笔记--14. Longest Common Prefix

为什么报错啊？？？错误信息如下：（这个错误的测试案例是[],有内容的能通过）

Line 933: Char 34: runtime error: reference binding to null pointer of type 'struct value_type' (stl_vector.h)

14. Longest Common Prefix

Easy

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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.

class Solution {
public:
    string longestCommonPrefix(vector<string>& strs) {
        int n=strs.size();
        int m=strs[0].size();
        string ans="";
        int tp=0;
        if(strs.empty())return "";
        else{
            for(int i=1;i<=m;i++)
            {
                tp=0;
                string tpstr=strs[0].substr(0,i);
                for(int j=1;j<n;j++)
                {
                    if(strs[j].substr(0,i)==tpstr)tp++;
                }
                if(tp==(n-1))
                {
                    if(ans.length()<tpstr.length())ans=tpstr;
                }
            }
            return ans;
        }

    }
};