zoj 3816 2014牡丹江网赛 DFS

http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=5348

写的真痛苦，换了好几种写法还是不行，贪心贪不对.......

参考了http://www.cnblogs.com/njczy2010/p/3961614.html

思路：
首先枚举左边的每一位，然后枚举右边有几位和这一位相同，写着还是有些细节要注意的

//#pragma comment(linker, "/STACK:102400000,102400000")
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <iostream>
#include <iomanip>
#include <cmath>
#include <map>
#include <set>
#include <queue>
using namespace std;

#define ls(rt) rt*2
#define rs(rt) rt*2+1
#define ll long long
#define ull unsigned long long
#define rep(i,s,e) for(int i=s;i<e;i++)
#define repe(i,s,e) for(int i=s;i<=e;i++)
#define CL(a,b) memset(a,b,sizeof(a))
#define IN(s) freopen(s,"r",stdin)
#define OUT(s) freopen(s,"w",stdout)
const ll ll_INF = ((ull)(-1))>>1;
const double EPS = 1e-8;
const int INF = 100000000;
const int MAXN = 30;

ll n;
char num[MAXN];
char leftn[MAXN],rightn[MAXN];
int lenn;

void init()
{
    sprintf(num,"%lld",n);
    CL(leftn,0);
    CL(rightn,0);
    lenn=strlen(num);
    for(int i=0;i<lenn;i++)
        num[i]-='0';
}

ll cal(int l, int r)
{
    ll ret=0;
    for(int i=0;i<l;i++)
        ret=ret*10+(ll)leftn[i];
    for(int i=r-1;i>=0;i--)
        ret=ret*10+rightn[i];
    return ret;
}

ll dfs(int l, int r, int cur)
{
    ////////
    /*printf("## l=%d r=%d\n",l,r);
    for(int i=0;i<l;i++)
        putchar('0'+i);
    putchar('\n');
    for(int i=r-1;i>=0;i--)
       putchar('0'+i);
    putchar('\n');*/
    /////////
    ll ans=-1;
    if(l+r>lenn)return -1ll;
    if(l+r == lenn)
    {
        ans=cal(l,r);
        if(ans>=n)return -1;
        return ans;
    }
    int m= (cur==1) ?num[l]:9;
    for(int i=m;i>=0;i--)
    {
        ///
        //printf("*******i=%d m=%d\n",i,m);
        ////////
        leftn[l]=i;
        if( ( l==0 || (l>0&&leftn[l]!=leftn[l-1]) ) && !(l==0 && i==0) && (l+r+1!=lenn) )///
        {
            for(int k=1;k+l+r<=lenn;k++)///
            {
                rightn[k+r-1]=i;
                ans=max(ans, dfs(l+1,r+k,cur&&(m==i)));
            }
        }
        else
        {
                ans=max(ans, dfs(l+1, r, cur&&(m==i)));

        }

        if(ans>0)
            return ans;
    }
    return ans;
}

int main()
{
    //IN("H.txt");
    int ncase;
    scanf("%d",&ncase);
    while(ncase--)
    {
        scanf("%lld",&n);
        init();
        printf("%lld\n",dfs(0,0,1));
    }
    return 0;
}