题解 | #密码截取# 区间dp

#include <iostream>
using namespace std;
const int N = 2550;
bool dp[N][N]; 

int main() {
    string s;
    cin >> s;
    int n = s.length(), start = 0, maxLength = 1;

    for(int i = 0; i < n; i++) {
        dp[i][i] = true; 
        if(i < n-1 && s[i] == s[i+1]) {
            dp[i][i+1] = true; 
            start = i;
            maxLength = 2;
        }
    }

   
    for(int len = 3; len <= n; len++) {
        for(int i = 0; i <= n-len; i++) {
            int j = i + len - 1; 

            if(s[i] == s[j] && dp[i+1][j-1]) {
                dp[i][j] = true;
                start = i;
                maxLength = len;
            }
        }
    }

    cout << maxLength;
    return 0;
}