78. Longest Common Prefix【medium】

Given k strings, find the longest common prefix (LCP).

 

Example

For strings "ABCD", "ABEF" and "ACEF", the LCP is "A"

For strings "ABCDEFG", "ABCEFG" and "ABCEFA", the LCP is "ABC"

解法一：

class Solution {
public:    
    /**
     * @param strs: A list of strings
     * @return: The longest common prefix
     */
    int min(int a, int b) {
        return ((a < b) ? a : b);
    }
     
    int calCount(string & a, string & b) {
        int la = a.size();
        int lb = b.size();
        int count = 0;
        
        for (int i = 0; i < la && i < lb; ++i) {
            if (a[i] == b[i]) {
                count++;
            } else {
                return count;
            }
        }
    }
     
    string longestCommonPrefix(vector<string> &strs) {
        int count = INT_MAX;
        int size = strs.size();
        
        if (size == 0) {
            return "";
        }
        
        for (int i = 0; i < strs.size() - 1; ++i) {
            count = min(calCount(strs[i], strs[i + 1]), count);
        }
        
        return strs[0].substr(0, count);
    }
};

解法二：

class Solution {
public:    
    /**
     * @param strs: A list of strings
     * @return: The longest common prefix
     */
    string longestCommonPrefix(vector<string> &strs) {
        if (strs.size() == 0) {
            return "";
        }
        
        string prefix = "";
        for (int i = 0; i < strs[0].length(); i++) {
            for (int j = 1; j < strs.size(); j++) {
                if (strs[j][i] != strs[0][i]) {
                    return prefix;
                }
            }
            prefix += strs[0][i];
        }
        
        return prefix;
    }
};