LeetCode题解：Longest Palindromic Substring

Longest Palindromic Substring

Given a string S, find the longest palindromic substring in S. You may assume that the maximum length ofS is 1000, and there exists one unique longest palindromic substring.

思路：

只想到一个O(n^2)的解法。就是从左到右扫描起点，同时从右向左扫描终点。也可以考虑记录从右向左各个字符的位置，方便搜索。

题解：

class Solution {
public:
bool check_palindrome(string& s, int i, int j)
{
while(i<j) if (s[i++]!=s[j--]) return false;
return true;
}

string longestPalindrome(string s) {
int i=0;
int j=s.size()-1;

int maxlen=0;
int start=0;

while(i<s.size())
{
j=s.size()-1;
while(j>=i)
{
if (s[j]==s[i])
if (check_palindrome(s,i,j))
{
if (maxlen<=j-i+1)
{
maxlen=j-i+1;
start=i;
}
break;
}
j--;
}
i++;
}
return s.substr(start, maxlen);
}
};