LeetCode 14. Longest Common Prefix

https://leetcode.com/problems/longest-common-prefix/description/

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

• Solution里提供了几种方法：横向扫描，纵向扫描，分治，二叉树搜索
• 我这用的纵向扫描所有字符串，只要找到这些串里第一个不匹配的字符，就找到最长公共前缀
• 注意此题与最长公共前缀短语的区别（http://www.cnblogs.com/pegasus923/p/5602046.html）
• 注意之前使用"i > strs[j].size() - 1"代替"i == strs[j].size()"，结果出错out of range。因为string.size()是size_t类型，所以size()为0时，"strs[j].size() - 1"会变成"-1 + INTMAX"
• 注意substr的用法
  • string::substr - C++ Reference
    • http://www.cplusplus.com/reference/string/string/substr/

//
//  main.cpp
//  LeetCode
//
//  Created by Hao on 2017/3/16.
//  Copyright © 2017年 Hao. All rights reserved.
//

#include <iostream>
#include <cstring>
#include <vector>
using namespace std;

class Solution {
public:
    string longestCommonPrefix(vector<string>& strs) {
        // Empty vector
        if (strs.empty()) return "";
        
        // Vertical scanning
        for (auto i = 0; i < strs[0].size(); i ++) {
            for (auto j = 1; j < strs.size(); j ++) {
                // Find the first string not matched
                // Do not use "i > strs[j].size() - 1" as it's of type size_t, 0 - 1 = INT_MAX rather than -1
                if (i == strs[j].size() || strs[j].at(i) != strs[0].at(i))
                    return strs[0].substr(0, i);
            }
        }
        
        return strs[0];
    }

};

int main(int argc, char* argv[])
{
    Solution    testSolution;
    string      result;
    
    vector<vector<string>> sVec = {{"abab","aba",""}, {"test a short phrase", "test a slightly longer phrase"}};

    /*
     ""
     "test a s"
     */
    for (auto str : sVec) {
        result = testSolution.longestCommonPrefix(str);
        
        cout << result << endl;
    }

    return 0;
}