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 == 0) {
            // bug 2: should not return null.
            return "";
        }
        
        // Find out the shortest length.
        String s0 = strs[0];
        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 = 0; i < len; i++) {
            // Bug 1: forget to write charAt(i);
            char c = s0.charAt(i);
            for (int j = 0; j < strs.length; j++) {
                if (strs[j].charAt(i) != c) {
                    // Bug 5: write substring to sbustring
                    return s0.substring(0, i);
                }                
            }
        }
        
        // Never break, means strs[0].0-len is the solution.
        return s0.substring(0, 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