Leetcode 之 Longest Common Prefix

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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.

Answer1 基于遍历的算法：

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];
    }
}

Answer2 基于剪切匹配串的算法

class Solution {
    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.equals("")) {
            return "";
        }
        return prefix;
    }
}

Answer3 基于分治与递归的算法

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if(strs.length == 0 ||strs == null){
            return "";
        }
        return longComPredix(strs,0,strs.length-1);
    }
    public String longComPredix(String[] strs, int l , int r){
        if(l==r){
            return strs[l];
        }else {
            int m = (l+r)/2;
            String lStr = longComPredix(strs,l,m);
            String rStr = longComPredix(strs,m+1,r);
            return longComPredix(lStr,rStr);
        }
    }
    public String longComPredix(String str1,String str2){
        if(str1.length()==0 || str2.length()==0){
            return "";
        }
        int min = Math.min(str1.length(),str2.length());
        for(int i = 0;i<min;i++){
            if(str1.charAt(i)!=str2.charAt(i)){
                return str1.substring(0,i);
            }
        }
        return str1.substring(0,min);
    }
}