1040 Longest Symmetric String (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:
11

一个简单的bp：
假设已有一段S已经获得其的symmetric长度为K，那么其后再加一个字符组成一个新的串的symmetric长度只有可能+1或+2或者重算（具体自己画个图思考一下）。

#include 
#include 
#include 
#include 
#include 
#include 
#include 

using namespace std;

const int maxn = 1005;
int bp[maxn];

int main() {
    memset(bp, 0, sizeof(bp));
    string str;
    getline(cin, str);
    // cout << str << endl;

    int cnt = 0;
    
    bool in_plus1_state = true;
    for(int i = 0; i < str.size(); ++i) {
        if (i == 0) {
            bp[i] = cnt = 0;
            continue;
        }
        if (str[i] == str[i-(cnt + 1)]) { // 加 1 的那种状况
            bp[i] = bp[i-1] + 1;
            in_plus1_state = true;
        }
        if (in_plus1_state && (i - (cnt + 2) >= 0 && str[i] == str[i - (cnt + 2)])) {
            bp[i] = bp[i-1] + 2;
            in_plus1_state = false;
        } else if (!in_plus1_state) {
            if (str[i] == str[i - (cnt + 2)]) {
                bp[i] = bp[i-1] + 2;
                in_plus1_state = false;
            } else {
                if (str[i] == str[i-1]) {
                    bp[i] = 1;
                    in_plus1_state = true;
                } else if (str[i] == str[i-2]) {
                    bp[i] = 2;
                    in_plus1_state = false;
                }
            }
        }
        cnt = bp[i];
    }
    int maxbp = 0;
    for(int i = 0;  i < str.size(); ++i) {
        maxbp = max(maxbp, bp[i]);
        // printf("%d ", bp[i]);
    }
    // printf("\n");
    cout << maxbp + 1 << endl;
    return 0;
}