POJ2402 Palindrome Numbers第K个回文数——找规律

问题

给一个数k，给出第k个回文数  链接

题解

打表找规律，详见https://www.cnblogs.com/lfri/p/10459982.html，差别仅在于这里从1数起.

AC代码

#include<cstdio>
#include<iostream>
#include<string>
#include<sstream>
using namespace std;

typedef long long LL;

void solve(string str)
{
    int len = str.length();

    if (len == 1)
    {
        printf("%c\n", str[0] - 1);
        return;
    }

    if (str[0] == '1')
    {
        if (str[1] == '0')
        {
            str[1] = '9';
            for (int i = 1; i < len; i++)  printf("%c", str[i]);
            for (int i = len - 2; i >= 1; i--)  printf("%c", str[i]);
            printf("\n");
        }
        else
        {
            for (int i = 1; i < len; i++)  printf("%c", str[i]);
            for (int i = len - 1; i >= 1; i--)  printf("%c", str[i]);
            printf("\n");
        }
    }
    else
    {
        str[0] = str[0] - 1;
        for (int i = 0; i < len; i++)  printf("%c", str[i]);
        for (int i = len - 2; i >= 0; i--)  printf("%c", str[i]);
        printf("\n");
    }
}

void ToString(LL num, string& str)
{
    stringstream ss;
    ss << num;
    ss >> str;
}

string str;
LL num;

int main()
{

    while (cin >> num && num)
    {
        ToString(num + 1, str);   //从1开始num要加一，从0开始不用
        solve(str);
    }
    return 0;
}