1040. Longest Symmetric String (25)

Given a string, you are supposed to output the length of the longest symmetric sub-string. For example, given "Is PAT&TAP symmetric?", the longest symmetric sub-string is "s PAT&TAP s", hence you must output 11.

Input Specification:

Each input file contains one test case which gives a non-empty string of length no more than 1000.

Output Specification:

For each test case, simply print the maximum length in a line.

Sample Input:

Is PAT&TAP symmetric?

Sample Output:

11

IDEA

1.遍历每个字符，以它为中心，判断：

若回文为奇数个数，则判断s[i] 两侧字符是否相等

若回文为偶数个数，则判断s[i]与右侧字符是否相等



CODE

#include<iostream>
#include<cstring>
using namespace std;
int main(){
string s;
getline(cin,s);
int max=1;
for(int i=0;i<s.size();i++){
int p=i-1,q=i+1;
while(p>=0&&q<s.size()){//回文是奇数个
if(s[p]==s[q]){
if(max<q-p+1){
max=q-p+1;
}
p--;
q++;
}else{
break;
}
}
}
for(int i=0;i<s.size();i++){//回文是偶数
int p=i,q=i+1;
while(p>=0&&q<s.size()){
if(s[p]==s[q]){
if(max<q-p+1){
max=q-p+1;
}
p--;
q++;
}else{
break;
}
}
}
cout<<max;
return 0;
}