华为笔试题--最长公共子串

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;
//最长公共子串
class Solution {
public:
    int longestSubstring(string x, string y) {
        if (x.size() > y.size()) swap(x, y); // 题目要求短串优先
        vector<vector<int> > f(x.size() + 1, vector<int>(y.size() + 1));
        int max = 0, pos = 0;
        
        for (int i = 1; i <= x.size(); i++) {
            for (int j = 1; j <= y.size(); j++) {
                if (x[i - 1] != y[j - 1]) f[i][j] = 0;
                else f[i][j] = f[i - 1][j - 1] + 1;
                if (max < f[i][j]) { // 细节：不能有等号 因为多个答案只取短串中最早出现的子串
                    max = f[i][j];
                    pos = i;
                }
            }
        }
        cout << x.substr(pos - max, max) << endl;
        return max;
    }
};

int main()
{
    string x, y;
    while (cin >> x >> y) {
        Solution().longestSubstring(x, y);
    }
    return 0;
}