题意:
定义: an+1=an+minDigit(an)×maxDigit(an)。
给定 a1 和 k,求 ak ?
题目:
Let’s define the following recurrence:
an+1=an+minDigit(an)⋅maxDigit(an).
Here minDigit(x) and maxDigit(x) are the minimal and maximal digits in the decimal representation of x without leading zeroes. For examples refer to notes.
Your task is calculate aK for given a1 and K.
Input
The first line contains one integer t (1≤t≤1000) — the number of independent test cases.
Each test case consists of a single line containing two integers a1 and K (1≤a1≤1018, 1≤K≤1016) separated by a space.
Output
For each test case print one integer aK on a separate line.
Example
Input
8
1 4
487 1
487 2
487 3
487 4
487 5
487 6
487 7
Output
42
487
519
528
544
564
588
628
Note
a1=487
a2=a1+minDigit(a1)⋅maxDigit(a1)=487+min(4,8,7)⋅max(4,8,7)=487+4⋅8=519
a3=a2+minDigit(a2)⋅maxDigit(a2)=519+min(5,1,9)⋅max(5,1,9)=519+1⋅9=528
a4=a3+minDigit(a3)⋅maxDigit(a3)=528+min(5,2,8)⋅max(5,2,8)=528+2⋅8=544
a5=a4+minDigit(a4)⋅maxDigit(a4)=544+min(5,4,4)⋅max(5,4,4)=544+4⋅5=564
a6=a5+minDigit(a5)⋅maxDigit(a5)=564+min(5,6,4)⋅max(5,6,4)=564+4⋅6=588
a7=a6+minDigit(a6)⋅maxDigit(a6)=588+min(5,8,8)⋅max(5,8,8)=588
分析:
显然当 an 中包含了 0 时,之后的数都等于 an。那么我们就要判断是否一定会出现包含 0 的情况,并且复杂度是可以接受的。想到只要出现0那就美滋滋,毕竟后面怎么加都是0,就不用看了。而0在1000次以内一定会出现,这个其实是有官方证明的,但是我更倾向于打表然后找找规律。
首先 minDigit(x)×maxDigit(x)≤81。那么令 t=x mod 1000,那么 t<1000,那么在经过递增过后,一定会出现 t+m≥1000,由于 m≤81,那么 t+m<1100,也就是一千零几,那么他的百位一定是 0。所以我们是可以直接循环去解决。
AC代码
#include <cstring>
#include <cstdio>
#include <algorithm>
using namespace std;
typedef long long ll;
ll dfs(ll x)
{ll m1=10,m2=0;while(x>0){ll y=x%10;x/=10;m1=min(m1,y);m2=max(m2,y);}return m1*m2;
}
int main()
{int t;scanf("%d",&t);while(t--){ll a,k;scanf("%lld%lld",&a,&k);k--;while(k--){ll y=dfs(a);if(y==0)break;a+=y;}printf("%lld\n",a);}
}