Leetcode Longest Palindromic Substring 5

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

Example:

Input: “babad”

Output: “bab”

Note: “aba” is also a valid answer.

Example:

Input: “cbbd”

Output: “bb”

题目链接

定义

dp[i][j] = 1 如果s[i,,,j]是回文串

＝ 0 如果s[i,,,j]不是回文串

dp[i][j] = 1 if i==j

= (s[i] == s[j]) if j==i+1

= (s[i] == s[j]) && dp[i+1][j-1] if j>i+1

class Solution {
public:
string longestPalindrome(string s) {
int len=s.length();
if(len==0||len==1) return s;

int dp[len][len];
for(int i=0;i<len;i++){
for(int j=0;j<len;j++)
dp[i][j]=0;
}

int max_=0;
int start=0,end=0;

for(int i=0;i<len;i++){
for(int j=0;j<i;j++){
if(i-j<2){
dp[j][i]=(s[i]==s[j]);
}
else{
dp[j][i]=((s[i]==s[j])&&(dp[j+1][i-1]));
}

if(dp[j][i]){
int ll=i-j+1;
if(max_<ll) {
max_=ll;
start=j;
end=i;
}
}
}
dp[i][i]=1;
}

return s.substr(start,end-start+1);

}
};