k进制高精加法

char sixt[20] = "0123456789ABCDEF";
string add(int k, string b) { //高精度加法过程，推广到 k 进制
    string a = b;
    reverse(a.begin(), a.end());
    int numa[maxN], numb[maxN], numc[maxN];
    int len = a.length(), lenc = 1;
    string ans;
    for (int i=0; i<len; i++) {
        if (isdigit(a[i])) numa[len-i] = a[i] - '0'; //对于十六进制的特判，如果是数字减去 0 ，下同
        else numa[len-i] = a[i] - 'A' + 10; //如果不是数字减去 A 再加上 10
        if (isdigit(b[i])) numb[len-i] = b[i] - '0';
        else numb[len-i] = b[i] - 'A' + 10;
    }
    int x = 0;
    while (lenc <= len) {
        numc[lenc] = numa[lenc] + numb[lenc] + x;
        x = numc[lenc] / k; //把除以 10 修改为除以 k
        numc[lenc] %= k; //这里把对 10 取模修改为对 k 取模
        lenc++;
    }
    numc[lenc] = x;
    while (numc[lenc] == 0) lenc--;
    for (int i=lenc; i>=1; i--) ans += sixt[numc[i]];
    return ans;
}