Longest Common Prefix

Write a function to find the longest common prefix string amongst an array of strings.

思路:

先求前两个字符串的公共前缀，然后拿这个前缀和其他字符串进行比对。

    int min(int a, int b){
        if(a < b)
            return a;
        return b;
    }
    string longestCommonPrefix(vector<string> &strs) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        int n = strs.size();
        if(n == 0)
            return "";
        if(n == 1)
            return strs[0];
        string s1 = strs[0], s2 = strs[1];
        int i = 0, j;
        string result = "";
        while(s1[i] == s2[i] && i < min(s1.length(), s2.length())){
            result += s1[i];
            i++;
        }
        for(j = 2; j < n; j++){
            s1 = strs[j];
            i = min(s1.length(), i);
            while(s1[i-1] != result[i-1] && i>0){
                i--;
            }
        }
        result = result.substr(0,i);
        return result;
    }

 另外一种方法是，依次增加result的长度，判断所有的string在这个位是不是相等。虽然复杂度不变，但是代码变得简练很多。

    string longestCommonPrefix(vector<string> &strs) {
        int n = strs.size();
        if(n == 0)
            return "";
        if(n == 1)
            return strs[0];
        int i, j;
        string result = "";
        for(i = 0;;i++){
            for(j = 1; j < n; j++){
                if(strs[j].length() < i+1 || strs[j][i] != strs[0][i])
                    break;
            }
            if(j < n)
                break;
            result += strs[0][i];
        }
        return result;
    }