LeetCode: Longest Common Prefix 解题报告

Longest Common Prefix

Write a function to find the longest common prefix string amongst an array of strings.

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SOLUTION 1:

解法很直观。先找到最小长度，然后逐个字母遍历，同时逐个遍历所有的字符串。注意各种小细节：

1. break的时候，应该返回上一个索引指向的子串。

2. 如果没有break，表示minlen长度的字串就是最大pre.

 public class Solution {
     //http://blog.csdn.net/fightforyourdream/article/details/14642079
     public String longestCommonPrefix(String[] strs) {
         if (strs == null || strs.length == ) {
             // bug 2: should not return null.
             return "";
         }

         // Find out the shortest length.
         String s0 = strs[];
         int len = s0.length();
         for (String s: strs) {
             len = Math.min(len, s.length());
         }

         // The index of the character which is examing.
         // Bug 3: 当不会break的时候，结果是错的
         // Bug 4: forget to add int i = 0;
         for (int i = ; i < len; i++) {
             // Bug 1: forget to write charAt(i);
             char c = s0.charAt(i);
             for (int j = ; j < strs.length; j++) {
                 if (strs[j].charAt(i) != c) {
                     // Bug 5: write substring to sbustring
                     return s0.substring(, i);
                 }
             }
         }

         // Never break, means strs[0].0-len is the solution.
         return s0.substring(, len);
     }
 }

2015.1.2 redo:

 public class Solution {
     public String longestCommonPrefix(String[] strs) {
         String ret = "";
         if (strs == null || strs.length == 0) {
             return ret;
         }

         int minLen = Integer.MAX_VALUE;
         for (String str: strs) {
             minLen = Math.min(str.length(), minLen);
         }

         for (int i = 0; i < minLen; i++) {
             for (int j = 1; j < strs.length; j++) {
                 if (strs[0].charAt(i) != strs[j].charAt(i)) {
                     return strs[0].substring(0, i);
                 }
             }
         }

         return strs[0].substring(0, minLen);
     }
 }

GITHUB:

https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/string/LongestCommonPrefix_1221_2014.java