暴力求解最长公共子串

#include <iostream>
#include <string>
using namespace std;

string longestStr(string str1, string str2) {
    int len1 = str1.size();
    int len2 = str2.size();
    int i, j;
    int max = 0, num = 0, start = 0;
    for (i = 0; i < len1; ++i) {
        for (j = 0; j < len2; ++j) {
            int start1 = i;
            int start2 = j;
            while ((start1 < len1 - 1)&&(start2 <= len2 -  1) && (str1[start1++] == str2[start2++])) {
                num++;
            }
            if (num > max) {
                max = num;
                start = i;
            }
            num = 0;
        }

    }
    string str;
    str = str1.substr(start, max);
    return str;
}

int main() {
    string str1 = "abccade";
    string str2 = "agbccaar";
    string str = longestStr(str1, str2);
    cout << str << endl;
    return 0;
}