C++双指针，速度超过dp | #最长公共子串#

class Solution {

public:

/**
* 双指针
*/
string LCS(string str1, string str2) {
    int first = 0, second = 0;

	int maxLen = 0;
	string res;
	while (second < str1.size()) {
		string subStr = str1.substr(first, second - first + 1);
		if (str2.find(subStr) != string::npos) {
			if (subStr.size() > maxLen) {
				maxLen = subStr.size();
				res = subStr;
			}
			second++;
		} else {
			if (second == first) {
				second ++;
				first ++;
			} else if (first < second) {
				first ++;
			}
		}
	}

	return res;
}

};