14. Longest Common Prefix

 1 class Solution {
 2 public:
 3     string longestCommonPrefix(vector<string>& strs) {
 4         string str;
 5         if (strs.size() == 0) return str;
 6         // if (strs.size() == 1) return strs[0];
 7         int count = 0;
 8         bool flag = true;
 9         for (size_t i = 0; i < strs[0].size(); ++ i) {
10             for (size_t j = 1; j < strs.size(); ++ j) {
11                 if (i >= strs[j].size() || strs[j][i] != strs[0][i]) {
12                     flag = false; break;
13                 }
14             }
15             if (flag) ++ count;
16         }
17         str = string(strs[0].begin(), strs[0].begin() + count);
18         return str;
19     }
20 };