洛谷 U3348 A2-回文数

#include <cstring>
#include <cstdio>
typedef long long LL;
struct node
{
    int a[50],len;
    node()
    {
        memset(a,0,sizeof(a));len=0;
    }
}Ret,RetS;
node findhws(LL n)
{
    LL ret,cnt=0,w=0,num=9,half=1;
    for(;1;)
    {
        if(w>0&&w%2==0) num*=10;
        w++;
        if(cnt+num>=n) break;
        cnt+=num;
    }
    n=n-cnt-1;
    for(int i=1;i<=w-1>>1;++i) half*=10;//赵基数
    half+=n;
    ret=half;
    if(w%2==1) half/=10;
    for(;ret;ret/=10) Ret.a[++Ret.len]=ret%10;
    RetS=Ret;
    for(int i=1;i<=RetS.len;++i) Ret.a[RetS.len-i+1]=RetS.a[i];
    for(;half;half/=10) Ret.a[++Ret.len]=half%10;
    return Ret;
}
LL n,len;
int main()
{
    scanf("%lld",&n);
    node ans=findhws(n);
    for(int i=1;i<=ans.len;++i) printf("%d",ans.a[i]);
    return 0;
}