LeetCode #14: Longest Common Prefix (C/C++).

easy

source: https://leetcode.com/problems/longest-common-prefix/
C/C++ Solution to LeetCode problem 14. Longest Common Prefix.

Problem

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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 “”.

Examples

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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.

Constraints

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• 1 <= strs.length <= 200
• 0 <= strs[i].length <= 200
• strs[i] consists of only lowercase English letters.

Solution

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• We start our longest prefix with the first word.
• Starting from the second word:
  • We set our prefix size to the size of the shortest word (current vs prefix –> min(prefix.size(), currentword.size())).
  • Once prefix and current word have the minimun size, we start comparing every charachter, once they are different, to that point is the size of our max prefix.
  • If the prefix size becomes 0, then no need to process the next words.

class Solution {
public:
  string longestCommonPrefix(vector<string>& strs) {
    string result = strs[0];

    for (int i=1; i<strs.size(); i++) {
      result = result.substr(0, min(result.size(), strs[i].size()));
      for (int p=0; p<result.size(); p++){
        if (strs[i][p] != result[p]) {
          result = result.substr(0, p);
          break;
        }
      }
      if (result.size() == 0)
        return "";
    }

    return result;
  }
};