LeetCode 14. Longest Common Prefix

Description

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

Note

All given inputs are in lowercase letters a-z.

Code

• java

class Solution {
    public String longestCommonPrefix(String[] strs) {
        int len = strs.length;
        if(len == 0) return "";
        int commonLength = 0;
        int minLength = strs[0].length();
        for(int i = 1; i < len; i++) {
            minLength = Math.min(minLength, strs[i].length());
        }
        for(; commonLength < minLength; commonLength++) {
            char ch = strs[0].charAt(commonLength);
            boolean same = true;
            for(int i = 1; i < len; i++) {
                if(strs[i].charAt(commonLength) != ch) {
                    same = false;
                    break;
                }
            }
            if(!same) break;
        }
        return strs[0].substring(0, commonLength);
    }
}

• Official solution1
• 按两个之间比较后得到的结果与下一个字符串继续比较。

 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;
}

• Official Solution2：Vertical scanning

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || 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];
    }
}

Conclusion

• 有很多种解法，比如二分，归并等