标签：tmp 转化 view ecif which include algo cat 序列
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.
Each input file contains one test case which gives a non-empty string of length no more than 1000.
For each test case, simply print the maximum length in a line.
Is PAT&TAP symmetric?
11
题目思路：这个题实质是求最长回文子串的长度。
有两种思路，第一种是以中间元素为中心，向两边扩散，这种写法及其好写，但是麻烦的是遇到abba这种偶数个回文串的情况就不知道怎么办了。在网上找到了一个神奇的方法，就是往每个字符串两边添加一个字符，之后再将总数除以2即可
这是该思路的链接https://blog.csdn.net/sunbaigui/article/details/8656933
贴一下我写的代码：
#include <iostream>
#include <string>
using namespace std;
int main(int argc, char *argv[]) {
string so;
getline(cin,so);
int length = so.length();
string s;
for(int i=0;i<length;i++)
{
s.push_back(‘-‘);
s.push_back(so[i]);
}
s.push_back(‘-‘);
int max = -1;
for(int i=1;i<s.length()-1;i++)
{
int tmp_length=1;
int p,q;
p = i-1;
q = i+1;
while (s[p] == s[q])
{
p--;
q++;
tmp_length+=2;
if(p<0||q>s.length())
break;
}
if(max<tmp_length)
max = tmp_length;
}
cout<<max/2;
}
第二种思路就是把串翻转过来，转化成求两个串最大子序列的问题（一般都有板子的）这里借鉴了（https://blog.csdn.net/zhangpiu/article/details/50733603）
#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
using namespace std;
string maxSubString(string s1, string s2){
int xlen = (int)s1.size(), ylen = (int)s2.size();
vector<vector<int>> m(xlen, vector<int>(ylen, 0));
int maxlen = -1, index = -1;
for(int i = 0; i < xlen; ++i){
for(int j = 0; j < ylen; ++j){
if(s1[i] == s2[j]){
if(i == 0 || j == 0) m[i][j] = 1;
else m[i][j] = m[i-1][j-1] + 1;
if(maxlen < m[i][j]){
maxlen = m[i][j];
index = i - maxlen + 1;
}
}
}
}
return s1.substr(index, maxlen);
}
int main(){
string s;
getline(cin, s);
string rs(s);
reverse(begin(rs), end(rs));
cout << maxSubString(s, rs).size();
return 0;
浙大pat1040 Longest Symmetric String（25 分）
标签：tmp 转化 view ecif which include algo cat 序列
原文地址：https://www.cnblogs.com/SK1997/p/9588868.html
