14. Longest Common Prefix

Problem:

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：

先求出最短的字符长度,然后从第一个字符串的第一个字符开始,判断是不是所有字符串的对应位字符相等,然后依次比较剩下的字符。这种解法思路很简单,相应的,性能也很低。

Solution (C++):

string longestCommonPrefix(vector<string>& strs) {
    if (strs.empty()) return "";

    int min_len = INT_MAX;

    for (auto str: strs)  {
        if (str.size() < min_len)
            min_len = str.size();
    }

    string pre = "";
    bool flag = true;

    for (int i = 0; i < min_len; ++i) {
        char a = strs[0][i];
        for (auto str: strs) {
                if (str[i] != a) { flag = false; break; }
        }
        if (flag) 
            pre += a;
    }

    return pre;
}

性能：

Runtime: ms  Memory Usage: MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB