hdu1023 Train Problem II

结题思路很容易想到递归，用记忆化搜索方式寻找答案。

由于ans可能非常大，用c++需要自己写加法器。

acm.hdu.edu.cn/showproblem.php?pid=1023

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4
 5 using namespace std;
 6 typedef __int64 LL;
 7 const int maxn = 150 + 10;
 8 char buffer[maxn * maxn][maxn];
 9 LL f[maxn][maxn];
10 int n, N;
11
12 void add(int lhs, int rhs, int dest){
13     int d = 0;
14     for(int i = maxn - 2; i >= 0; i--){
15         int j = buffer[lhs][i] + buffer[rhs][i] + d;
16         buffer[dest][i] = j % 10;
17         d = j / 10;
18     }
19 }
20
21 int solve(int s, int q){
22     if(f[s][q] != -1) return f[s][q];
23     if(!q) return f[s][q] = 0;
24     if(s){
25         int l1 = solve(s + 1, q - 1), l2 = solve(s - 1, q);
26         add(l1, l2, N);
27         N++;
28         return f[s][q] = N - 1;
29     }
30     return f[s][q] = solve(s + 1, q - 1);
31 }
32
33 void print(int i){
34     int low = maxn - 1;
35     for(int j = 0; j < maxn - 1; j++){
36         if(buffer[i][j]){
37             low = j;
38             break;
39         }
40     }
41     for(int j = low; j < maxn - 1; j++) putchar(buffer[i][j] + ‘0‘);
42     putchar(‘\n‘);
43 }
44
45 int main(){
46     memset(f, -1, sizeof f);
47     memset(buffer, 0, sizeof buffer);
48     buffer[0][maxn - 2] = 1;
49     N = 1;
50     while(~scanf("%d", &n)){
51         int ans = solve(0, n);
52         print(ans);
53     }
54     return 0;
55 }