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

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;
typedef __int64 LL;
const int maxn = 150 + 10;
char buffer[maxn * maxn][maxn];
LL f[maxn][maxn];
int n, N;

void add(int lhs, int rhs, int dest){
    int d = 0;
    for(int i = maxn - 2; i >= 0; i--){
        int j = buffer[lhs][i] + buffer[rhs][i] + d;
        buffer[dest][i] = j % 10;
        d = j / 10;
    }
}

int solve(int s, int q){
    if(f[s][q] != -1) return f[s][q];
    if(!q) return f[s][q] = 0;
    if(s){
        int l1 = solve(s + 1, q - 1), l2 = solve(s - 1, q);
        add(l1, l2, N);
        N++;
        return f[s][q] = N - 1;
    }
    return f[s][q] = solve(s + 1, q - 1);
}

void print(int i){
    int low = maxn - 1;
    for(int j = 0; j < maxn - 1; j++){
        if(buffer[i][j]){
            low = j;
            break;
        }
    }
    for(int j = low; j < maxn - 1; j++) putchar(buffer[i][j] + '0');
    putchar('
');
}

int main(){
    memset(f, -1, sizeof f);
    memset(buffer, 0, sizeof buffer);
    buffer[0][maxn - 2] = 1;
    N = 1;
    while(~scanf("%d", &n)){
        int ans = solve(0, n);
        print(ans);
    }
    return 0;
}