14. Longest Common Prefix

1. Description

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 “”.

2. Example

Example 1

Input: strs = [“flower”,“flow”,“flight”]
Output: “fl”

Example 2

Input: strs = [“dog”,“racecar”,“car”]
Output: ""
Explanation: There is no common prefix among the input strings.

3. Constraints

• 1 <= strs.length <= 200
• 0 <= strs[i].length <= 200
• strs[i] consists of only lowercase English letters if it is non-empty.

4. Solutions

Vertical Scan

m = strs.size(), n = strs[0].size()
Time complexity: O(mn)
Space complexity: O(1)

class Solution {
public:
    string longestCommonPrefix(const vector<string> &strs) {
        int len = 0;
        for (bool matched = true; matched;) {
            for (int i = 0; i < strs.size(); ++i) {
                if (strs[i].size() == len || strs[i][len] != strs[0][len]) {
                    matched = false;
                    break;
                }
            }

            if (matched) {
                ++len;
            }
        }

        return strs.front().substr(0, len);
    }
};