_14.java

package com.fishercoder.solutions;

/**
 * 14. Longest Common Prefix
 *
 * 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.
 */

public class _14 {

    public static class Solution1 {
        //horizontal scan
        public String longestCommonPrefix(String[] strs) {
            if (strs.length == 0) {
                return "";
            }
            String prefix = strs[0];
            for (int i = 1; i < strs.length; i++) {
                while (strs[i].indexOf(prefix) != 0) {
                    prefix = prefix.substring(0, prefix.length() - 1);
                    if (prefix.isEmpty()) {
                        return "";
                    }
                }
            }
            return prefix;
        }
    }

    public static class Solution2 {
        //vertical scan
        public String longestCommonPrefix(String[] strs) {
            if (strs.length == 0) {
                return "";
            }
            for (int i = 0; i < strs[0].length(); i++) {
                char c = strs[0].charAt(i);
                for (int j = 1; j < strs.length; j++) {
                    if (i == strs[j].length() || strs[j].charAt(i) != c) {
                        return strs[0].substring(0, i);
                    }
                }
            }
            return strs[0];
        }
    }
}