链接:
原题:
Don't you think 162456723 very special? Look at the picture below if you are unable to find its speciality. ( a | b means ‘ b is divisible by a ’)
Figure: Super Numbers
Given n, m (0 < n < m < 30) , you are to find a m -digit positive integer X such that for every i (n <= i <= m), the first i digits of X is a multiple of i . If more than one such X exists, you should output the lexicographically smallest one. Note that the first digit of X should not be 0 .
Input
Output
For each test case, print the case number and X . If no such number, print -1 .
样例输入:
2
1 10
3 29
样例输出:
Case 1: 1020005640
Case 2: -1
题目大意:
所谓的超级数字,就是指一个数字,从左边位数开始, 前i位能被i整数
输入n, m, 第n为开始要满足超级数字的要求。
分析与总结:
这种题很容易想到直接暴力回溯可以求出答案,但是也赤裸裸地TLE了。。。(据说网上有人暴力回溯也擦边过了, 膜拜)
由于没想到好的减枝方法, 于是打表水过
直接暴力回溯,TLE了。。。求大神的高效算法啊
#include<iostream> #include<cstdio> #include<cstring> using namespace std; int str[35]; int n, m, flag; inline int mod(int *str,int num, int len){ int remainder=0; for(int i=0;i<len;i++) remainder=(remainder*10+str[i])%num; return remainder; } void search(int cur){ if(flag) return; if(cur==m){ flag=true; return; } for(int i=0; i<=9 && !flag; ++i){ if(cur==0 && i==0) continue; str[cur] = i; if(cur >= n-1){ // 大于等于n位的要求是倍数 if(mod(str, cur+1, cur+1)!=0) continue; } search(cur+1); if(flag) return; } } int main(){ int T, cas=1; scanf("%d",&T); while(T--){ scanf("%d%d",&n,&m); memset(str, 0, sizeof(str)); flag = 0; search(0); printf("Case %d: ", cas++); if(flag) { for(int i=0; i<m; ++i)printf("%d", str[i]); printf("\n"); } else printf("-1\n"); } return 0; }
打表的,罪过啊罪过:
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"-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","10000000000000000000000000086", "-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1","-1" }; int main(){ int T, cas=1; scanf("%d", &T); while(T--){ int n, m; scanf("%d%d",&n,&m); printf("Case %d: ",cas++); printf("%s\n", ans[n][m]); } }
—— 生命的意义,在于赋予它意义。
原创 http://blog.csdn.net/shuangde800 , By D_Double (转载请标明)