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.

Solution (Java)

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs.length < 1) {
            return "";
        }
        if (strs.length == 1) {
            return strs[0];
        }
        String temp = strs[0];
        int i = 1;
        String cur;
        while (temp.length() > 0 && i < strs.length) {
            if (temp.length() > strs[i].length()) {
                temp = temp.substring(0, strs[i].length());
            }
            cur = strs[i].substring(0, temp.length());
            if (!cur.equals(temp)) {
                temp = temp.substring(0, temp.length() - 1);
            } else {
                i++;
            }
        }
        return temp;
    }
}

Solution (Javascript)

/**
 * @param {string[]} strs
 * @return {string}
 */
var longestCommonPrefix = function(strs) {
  if (strs.length === 0) return '';
  var len1 = strs.length;
  var len2 = strs[0].length;
  var tmp = '';
  var res = '';
  outer: for (var i = 0; i < len2; i++) {
    tmp = strs[0][i];
    inner: for (var j = 1; j < len1; j++) {
      if (strs[j][i] !== tmp) break outer;
    }
    res += tmp;
  }
  return res;
};

Explain:

nope.

Complexity:

• Time complexity : O(n^2).
• Space complexity : O(1).