LeetCode#5. Longest Palindromic Substring

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example 1:

Input: "babad"
Output: "bab"
Note: "aba" is also a valid answer.
Example 2:

Input: "cbbd"
Output: "bb"

问题大意：在一个字符串中寻找最长的子字符串，该字符串是回数（即从左往右和从右往左读的结果是相同的）。

解题思路：遍历字符串，先找到回文最中间的部分aba或者bb,之后向两边搜索，更新长度和范围，找到长度最大的回文字符串。

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

int start = 0, len = 1;
void isPalindrome(const string &s, int a, int b) {
	while (a >= 0 && b < s.size() && s[a] == s[b]){
		a--;
		b++;
	}

	if (len < b - a - 1) {
		start = a + 1;
		len = b - a - 1;
	}
}

string longestPalindrome(string s) {
	if (s.size() < 2) return s;
	//int start = 0, len = 1;
	for (int i = 1; i < s.size(); i++) {
		isPalindrome(s, i - 1, i + 1);
		isPalindrome(s, i - 1, i);
	}
	return s.substr(start, len);
}

int main(){
	string s1 = "1234325234321";

	string result = longestPalindrome(s1);

	cout << "最长回文串是： " << result << endl;
	cout << "最长回文串长度是： " << len << endl;
	getchar();
}