#include <bits/stdc++.h>
using namespace std;

int cnt[256];
int pal[16];
int map2idx[256];

int hex2dec(char c){
    if(c>='0'&&c<='9') return c-'0';
    return 10+c-'A';
}

char dec2hex(int x){
    if(x<10) return '0'+x;
    return 'A'+(x-10);
}

bool cmp(int a,int b){
    if(cnt[a]!=cnt[b]) return cnt[a]>cnt[b];
    return a<b;
}

int main(){
    int n;cin>>n;
    vector<vector<int>> img(n);
    memset(cnt,0,sizeof cnt);
    for(int i=0;i<n;i++){
        string s;cin>>s;
        for(int j=0;j<(int)s.size();j+=2){
            int v=hex2dec(s[j])*16+hex2dec(s[j+1]);
            img[i].push_back(v);
            cnt[v]++;
        }
    }
    vector<int> all;
    for(int i=0;i<256;i++) if(cnt[i]>0) all.push_back(i);
    sort(all.begin(),all.end(),cmp);
    for(int i=0;i<16;i++) pal[i]=all[i];
    for(int g=0;g<256;g++){
        int best=0;
        for(int i=1;i<16;i++){
            int d1=abs(g-pal[i]);
            int d0=abs(g-pal[best]);
            if(d1<d0||(d1==d0&&i<best)) best=i;
        }
        map2idx[g]=best;
    }
    for(int i=0;i<16;i++){
        cout<<dec2hex(pal[i]/16)<<dec2hex(pal[i]%16);
    }
    cout<<endl;
    for(int i=0;i<n;i++){
        for(int v:img[i]) cout<<dec2hex(map2idx[v]);
        cout<<endl;
    }
    return 0;
}
//:)
//114514

虽然只有一种味道，但真的很 鲜~

葵花籽味

#include <cmath> //abs
#include <cstdio> //scanf, printf
#include <string> //string
#include <iostream> //cin
#include <algorithm> //sort
using namespace std;

int mp[25][25], choose[25]; //choose：找出的16个数字

class cnter
{
public:
    int num, cnt; //还要知道是什么数字，排序之后才不会乱
} cnt[260];

int main()
{
    int n;
    scanf("%d", &n);
    int m;
    for(int i=1;i<=n;i++)
    {
        string str;
        cin >> str;
        m = str.size()/2;
        for(int j=1;j<=m;j++)
        {
            char c1 = str[j*2-2], c2 = str[j*2-1];
            int a1, a2;
            if(c1 >= '0' && c1 <= '9') a1 = c1 - '0';
            else a1 = c1 - 'A' + 10;
            if(c2 >= '0' && c2 <= '9') a2 = c2 - '0';
            else a2 = c2 - 'A' + 10;
            mp[i][j] = a1*16+a2; //16 to 10
            cnt[mp[i][j]].cnt++; //计数++
            cnt[mp[i][j]].num = mp[i][j]; //设置数字
        }
    }
    sort(cnt, cnt + 256, [](cnter x, cnter y) { return x.cnt > y.cnt || x.cnt == y.cnt && x.num < y.num; }); //排序
    for(int i=0;i<16;i++)
    {
        choose[i] = cnt[i].num;
        int a = choose[i]/16, b = choose[i]%16;
        printf("%c%c", (a <= 9)?(a + '0'):(a + 'A' - 10), (b <= 9)?(b + '0'):(b + 'A' - 10)); //10 to 16
        //printf(":%d\n", cnt[i].cnt); //debug语句
    }
    putchar('\n');
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            int num = mp[i][j];
            int minn = 2147483647, mink;
            for(int k=0;k<16;k++)
            {
                if(abs(num - choose[k]) < minn)
                {
                    minn = abs(num - choose[k]);
                    mink = k;
                }
            }
            putchar(mink <= 9 ? mink+'0' : (mink + 'A' - 10)); //10 to 16
        }
        puts("");
    }
    return 0;
}