PAT 1040 Longest Symmetric String (25)

1040 Longest Symmetric String (25)（25 分）

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:

思路：

分别枚举子串开始的位置和子串的长度，需要注意的是子串对应位置下标的计算，假设开始位置为start，长度为len，与s[i]对应的字符是s[start+len-1-(i-start)]，画个示意图很容易就算出来了。

代码：

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <cctype>
#include <climits>
#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
using namespace std;bool symmetric(string s, int start, int len)
{for (int i = start; i < start + len / 2; i++){if (s[i] != s[start + len - 1 - (i - start)])return false;}return true;
}int main()
{string s;getline(cin, s);int maxlen = 1;for (int i = 0; i < s.length(); i++){for (int j = 1; j <= s.length() - i; j++){if (symmetric(s, i, j) && j > maxlen)maxlen = j;}}cout << maxlen << endl;return 0;
}

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