diff函数的实现——LCS的变种问题

　　昨天去去哪儿笔试，碰到了一个我们一直很熟悉的命令(diff——ubuntu下面)，可以比较字符串，即根据最长公共子串问题，如果A中有B中没有的字符输出形式如下(-ch),如果A中没有，B中有可以输出如下形式(+ch).

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

string LCS(string &s1, string &s2)
{
    int row = s1.size();
    int col = s2.size();
    string table[row + 1][col + 1];
    char rowChar[row + 1];
    char colChar[col + 1];
    int cnt = 0;
    rowChar[0] = colChar[0] = '';
    for(int i = row - 1, cnt = 1; i >= 0; i--, cnt++)
    {
        rowChar[cnt] = s1[i];
    }
    for(int i = col - 1, cnt = 1; i >= 0; i--, cnt++)
    {
        colChar[cnt] = s2[i];
    }
    char ch1, ch2;
    string str1, str2;
    for(int i = 1; i <= row; i++)
    {
        for(int j = 1; j <= col; j++)
        {
            ch1 = rowChar[i];
            ch2 = colChar[j];
            if(ch1 == ch2)
                table[i][j] = ch1 + table[i - 1][j - 1];
            else
            {
                str1 = table[i - 1][j];
                str2 = table[i][j - 1];
                if(str1.size() == str2.size())
                    table[i][j] = str1 < str2 ? str2 : str1;
                else
                    table[i][j] = str1.size() < str2.size() ? str2 : str1;
            }
        }
    }
    return table[row][col];
}
void showDiff(string &s1, string &s2, string sub, vector<string> &ret)
{
    cout << "Sub = " << sub << endl;
    int len1 = s1.size();
    int len2 = s1.size();
    for(int i = 0, j = 0; i < len1; i++)
    {
        if(s1[i] != sub[j])
        {
            string str;
            str.push_back('-');
            str.push_back(s1[i]);
            ret.push_back(str);
        }
        else
            j++;
    }
    for(int i = 0, j = 0; i < len2; i++)
    {
        if(s2[i] != sub[j])
        {
            string str;
            str.push_back('+');
            str.push_back(s2[i]);
            ret.push_back(str);
        }
        else
            j++;
    }
}

int main()
{
    string str1, str2;
    cin >> str1 >> str2;
    string retSub = LCS(str1, str2);
    vector<string> ret;
    showDiff(str1, str2, retSub, ret);
    vector<string>::iterator iter;
    for(iter = ret.begin(); iter != ret.end(); iter++)
        cout << *iter << endl;
    return 0;
}