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：

#include <bits/stdc++.h>

using namespace std;

int main() {
    string str;
    getline(cin, str);
    int p1, p2, temp, ans = 1;
    int len = str.length();
    for (int i = 0; i < len; ++i) {
        p1 = i;
        p2 = i + 1;
        temp = 0;
        while (p1 >= 0 && p2 < len) {
            if (str[p1--] == str[p2++])
                temp += 2;
            else
                break;
        }
        if (temp > ans) ans = temp;
    }
    for (int i = 0; i < len; ++i) {
        p1 = p2 = i;
        temp = -1;
        while (p1 >= 0 && p2 < len) {
            if (str[p1--] == str[p2++])
                temp += 2;
            else
                break;
        }
        if (temp > ans) ans = temp;
    }
    cout << ans << endl;
    return 0;
}