UVALive 2889 (数学)

题意:求第n大的回文数字.

截取对称中心前面的那一段数字,从大到小依次就是1,2,3......11,12,13......,100,101

而以某个数字为对称中心前一段的数字共有两种,比如13就有131和1331.

所以判断一下是哪一种就好了.

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <map>
#include <set>
#include <vector>
#include <queue>
using namespace std;

long long n;

void solve () {
long long cur = 1, cnt = n;
while (cnt > 2*(cur*10-cur)) cnt -= 2*(cur*10-cur), cur *= 10;
bool flag = (cnt <= cur*10-cur);
if (!flag) cnt -= (cur*10-cur);
cur = cur+cnt-1;
cout << cur;
if (flag) cur /= 10;
while (cur) {
cout << cur%10;
cur /= 10;
}
cout << "\n";
}

int main () {
while (cin >> n && n) {
solve ();
}
return 0;
}