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.

 1 public class Solution {

 2     //http://blog.csdn.net/fightforyourdream/article/details/14642079

 3     public String longestCommonPrefix(String[] strs) {

 4         if (strs == null || strs.length == 0) {

 5             // bug 2: should not return null.

 6             return "";

 7         }

 8         

 9         // Find out the shortest length.

10         String s0 = strs[0];

11         int len = s0.length();

12         for (String s: strs) {

13             len = Math.min(len, s.length());

14         }

15         

16         // The index of the character which is examing.

17         // Bug 3: 当不会break的时候，结果是错的

18         // Bug 4: forget to add int i = 0;

19         for (int i = 0; i < len; i++) {

20             // Bug 1: forget to write charAt(i);

21             char c = s0.charAt(i);

22             for (int j = 0; j < strs.length; j++) {

23                 if (strs[j].charAt(i) != c) {

24                     // Bug 5: write substring to sbustring

25                     return s0.substring(0, i);

26                 }                

27             }

28         }

29         

30         // Never break, means strs[0].0-len is the solution.

31         return s0.substring(0, len);

32     }

33 }

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2015.1.2 redo:

 1 public class Solution {

 2     public String longestCommonPrefix(String[] strs) {

 3         String ret = "";

 4         if (strs == null || strs.length == 0) {

 5             return ret;

 6         }

 7         

 8         int minLen = Integer.MAX_VALUE;

 9         for (String str: strs) {

10             minLen = Math.min(str.length(), minLen);

11         }

12         

13         for (int i = 0; i < minLen; i++) {

14             for (int j = 1; j < strs.length; j++) {

15                 if (strs[0].charAt(i) != strs[j].charAt(i)) {

16                     return strs[0].substring(0, i);

17                 }

18             }

19         }

20         

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

22     }

23 }

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GITHUB:

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