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

• 0 <= strs.length <= 200
• 0 <= strs[i].length <= 200
• strs[i] consists of only lower-case English letters.

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 prefix_length = 0;
        for (int i = 0, done = 1; done == 1; ++i, ++prefix_length) {
            for (int j = 0; j < strs.size(); ++j) {
                if (i >= strs[j].size() || strs[j][i] != strs[0][i]) {
                    done = 0;
                    break;
                }
            }
        }

        return string(strs[0].begin(), strs[0].begin() + prefix_length - 1);
    }
};