题解 | #[NOIP1999]回文数#

#include <stdio.h>
#include<string.h>
void SUM10(char* str1, char* str2, int len, int N)//N<=10
{
    int start = 0;
    int end = len - 1;
    int a = 0;
    int jw = 0;
    while (end >= 0)
    {
        str1[end] = str1[end] + jw;
        a = ((str1[end] - '0') + (str2[end] - '0')) % N;
        jw = ((str1[end] - '0') + (str2[end] - '0')) / N;
        str1[end] = a + '0';
        end--;
    }
    if (jw > 0)
    {
        int i = 0;
        for (i = len; i > 0; i--)
        {
            str1[i] = str1[i - 1];
        }
        str1[0] = jw + '0';
    }
}
void SUM16(char* str1, char* str2, int len,int N) //N>10
{
    int start = 0;
    int end = len - 1;
    int a = 0;
    int i = 0;
    int j = 0;
    int jw = 0;
    while (end >= 0)
    {
        if (str1[end] + jw > '9'&&str1[end]<'A')
        {
            str1[end] = 'A';
        }
        else
        {
            str1[end] += jw;
        }
        if (str1[end] >= 'A')
        {
            i = str1[end] - 'A' + 10;
        }
        else
        {
            i = str1[end] - '0';
        }
        if (str2[end] >= 'A')
        {
            j = str2[end] - 'A' + 10;
        }
        else
        {
            j = str2[end] - '0';
        }
        a = (i + j) % N;
        jw = (i + j) / N;
        if (a >= 10)
        {
            str1[end] = a - 10 + 'A';
        }
        else
        {
            str1[end] = a + '0';
        }
        end--;
    }
    if (jw > 0)//99位数字进1位 整体向后挪
    {
        int i = 0;
        for (i = len; i > 0; i--)
        {
            str1[i] = str1[i - 1];
        }
        str1[0] = '1';
    }
}
void fz_16(char* str1, char* str2, int len) //翻转字符数组
{
    int i = 0;
    while (i < len)
    {
        str2[len - 1 - i] = str1[i];
        i++;
    }
}
int is_hw(char* str, int len)  //判断是否回文 1是 0否
{
    int start = 0;
    int end = len - 1;
    while (start < end)
    {
        if (str[start] != str[end])
        {
            return 0;
        }
        else {
            start++;
            end--;
        }
    }
    return 1;
}
int main() {
    int N = 0;
    char M1[100] = { 0 };
    char M2[100] = { 0 };
    int STEP = 0;
    scanf("%d", &N);
    getchar();
    scanf("%s", M1);
    int len = (int)strlen(M1);
    while (is_hw(M1, len) != 1)
    {
        if (STEP == 30)
        {
            printf("Impossible!\n");
            return 0;
        }
        fz_16(M1, M2, len);
        if (N>10)
        {
            SUM16(M1, M2, len,N);
        }
        else {
            SUM10(M1, M2, len, N);
        }
        len = (int)strlen(M1);
        STEP++;
    }
    printf("STEP=%d\n", STEP);
    return 0;
}