1040 Longest Symmetric String

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

题意：

　　找出最长的对称子串。

思路：

　　遍历字符串，以字符串中的每一个字符为对称中心，向两边查找。因为不知道对称子串的长度是奇数还是偶数，所以两种情况都要考虑，取最大值。

Code：

 1 #include <bits/stdc++.h>
 2
 3 using namespace std;
 4
 5 int main() {
 6     string str;
 7     getline(cin, str);
 8     int p1, p2, temp, ans = 1;
 9     int len = str.length();
10     for (int i = 0; i < len; ++i) {
11         p1 = i;
12         p2 = i + 1;
13         temp = 0;
14         while (p1 >= 0 && p2 < len) {
15             if (str[p1--] == str[p2++])
16                 temp += 2;
17             else
18                 break;
19         }
20         if (temp > ans) ans = temp;
21     }
22     for (int i = 0; i < len; ++i) {
23         p1 = p2 = i;
24         temp = -1;
25         while (p1 >= 0 && p2 < len) {
26             if (str[p1--] == str[p2++])
27                 temp += 2;
28             else
29                 break;
30         }
31         if (temp > ans) ans = temp;
32     }
33     cout << ans << endl;
34     return 0;
35 }