codefroces204A - Little Elephant and Interval 数位DP

题意：给你n，m 问你n-m中有多少个数首位等于末位。

解题思路：数位DP，从0-n有多少个，这样分开计算，首先把每一位所有可能都枚举出来，然后在一位一位的比对DP

解题代码：

 1 // File Name: 204a.cpp
 2 // Author: darkdream
 3 // Created Time: 2014年07月25日 星期五 09时16分57秒
 4 
 5 #include<vector>
 6 #include<list>
 7 #include<map>
 8 #include<set>
 9 #include<deque>
10 #include<stack>
11 #include<bitset>
12 #include<algorithm>
13 #include<functional>
14 #include<numeric>
15 #include<utility>
16 #include<sstream>
17 #include<iostream>
18 #include<iomanip>
19 #include<cstdio>
20 #include<cmath>
21 #include<cstdlib>
22 #include<cstring>
23 #include<ctime>
24 #define LL long long
25 using namespace std;
26 LL sum[20];
27 LL temp[20];
28 LL count(LL n)
29 {
30    int len = 0;
31    LL k = n;
32    while(k)
33    {
34        len ++ ; 
35        k/= 10 ; 
36    }
37  //  printf("%d\n",len);
38    if(len == 1)
39        return n+1;
40    LL ans = sum[len-1];
41    int t = len ; 
42    int a[20];
43    while(n)
44    {
45       a[t] = n %10 ; 
46       n = n/10 ;
47       t--;
48    }
49    for(int i =1 ;i <= len-1;i ++)
50    {
51         int be; 
52         be = i == 1?1:0;
53         for(;be < a[i];be++)
54         {
55           ans += temp[len-i-1]; 
56         }
57    }
58    if(a[len] >= a[1])
59        ans ++ ; 
60    return ans; 
61 }
62 int main(){
63    LL n ,m;
64    temp[0] =1 ;
65    temp[1] = 10 ; 
66    for(int i =1 ;i <= 17 ;i ++)
67        temp[i] = temp[i-1]*10;
68    sum[0] = 1; 
69    sum[1] = 10; 
70    for(int i = 2 ;i <= 19 ;i ++)
71    {
72        sum[i] = sum[i-1];
73        for(int j = 1;j <= 9 ;j ++)
74               sum[i] += temp[i-2]; 
75    }
76   // printf("%I64d\n",count(1));
77    scanf("%I64d %I64d",&n,&m);
78    printf("%I64d",count(m)-count(n-1)); 
79 return 0;
80 }

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posted on 2014-07-25 11:18 dark_dream 阅读(260) 评论(0) 编辑收藏举报