LeetCode 7最长公共前缀

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs.length==0)return "";
        if (strs.length==1)return strs[0];
        int sameCharNum=0;
        Set<Integer> set=new HashSet<>();
        for (int i = 1; i < strs.length; i++) {
            sameCharNum = longestNum(strs[0], strs[i]);
            set.add(sameCharNum);
        }
        int minNum=Integer.MAX_VALUE;
        for (int i:set){
            if(minNum>i){
                minNum=i;
            }
        }
        return strs[0].substring(0,minNum);
    }

    public int longestNum(String s1,String s2){
        int sameCharNum=0;
        for (int i = 0; i<s1.length()&&i<s2.length(); i++) {
            if (s1.charAt(i)==s2.charAt(i)) {
                sameCharNum++;
            }else
                return sameCharNum;
        }
        return sameCharNum;
    }
}