可在范围 L 和 R 内的字符创建的最大长度回文子串

#include <bits/stdc++.h>
using namespace std;
#define N 4
 
//user-defined function to calculate frequencies
int calculateQueries(int m, int s, int p[N][26])
{
    m--;
    s--;
 
    // marking for odd frequency
    bool f = false;
 
    // counter variable to count the maximum length
    int cnt = 0;
 
    // Traversing all characters
    for (int x = 0; x < 26; x++) 
    {
        int cnt1 = p[s][x];
        if (m > 0)
            cnt1 -= p[m - 1][x];
 
        // finding odd frequencies
        if (cnt1 % 2 == 1) 
        {
            f = true;
            cnt += cnt1 - 1;
        }
     
        else
            cnt += cnt1;
    }
 
    if (f)
        cnt += 1;
 
    return cnt;
}
 
void calculateFreq(string str, int p[N][26])
{
    int m = str.size();
 
    // Iteration for counter variable
    for (int x = 0; x < m; x++)
    {
        p[x][str[x] - 'a']++;
    }
 
    for (int x = 1; x < m; x++)
    {
        for (int y = 0; y < 26; y++)
            p[x][y] += p[x - 1][y];
    }
}
 
// Code controller
int main()
{
    string str = "bbbbb";
 
    // prefix array
    int p[N][26];
    memset(p, 0, sizeof p);
    calculateFreq(str, p);
 
    int q[][2] = { 1, 4};
    int sq = sizeof(q) / sizeof(q[0]);

    for (int x = 0; x < sq; x++)
    {
        cout << calculateQueries(q[x][0],
                               q[x][1], p)
             << endl;
    }
 
    return 0;
}

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int maxLengthPalindrome(string& s, int st, int e) 
{
    // Initialize a vector to store the frequency of each character
    vector<int> freq(26, 0);

    // Count the frequency of characters within the given range
    for (int x = st - 1; x <= e - 1; x++)
    {
        freq[s[x] - 'a']++;
    }

    int l = 0;
    bool oddFreq = false;

    // Calculate the maximum length palindrome
    for (int x = 0; x < 26; x++)
    {
        l += freq[x] / 2 * 2;
        
        if (freq[x] % 2 == 1) 
        {
            oddFreq = true;
        }
    }

    // If there is a character with an odd frequency, increment the length by 1
    if (oddFreq) 
    {
        l++;
    }

    return l;
}

int main() 
{
    string s = "amem";
    int st = 1;
    int e = 4;

    int maxLen = maxLengthPalindrome(s, st, e);

    cout << "Maximum length palindrome: " << maxLen << endl;

    return 0;
}