HDU 1223 打表 + 大数

http://acm.hdu.edu.cn/showproblem.php?pid=1223

一般遇到这些题，我都是暴力输出前几项，找规律。未果。

然后输出n = 1时候，以A开始，有多少个答案，

n = 2的时候，A开始，B开始，有多少个答案。然后发现了规律。大数之

const int maxn = 50 + 20;
struct node {
    int val;
    int id;
    bool operator < (const struct node & rhs) const {
        if (val != rhs.val) return val < rhs.val;
        else return id < rhs.id;
    }
}a[maxn];
int n;
int f[maxn];
int lena;
map<string, bool>mp;
int aa;
void dfs(int cur) {
    if (cur == n + 1) {
        for (int i = 1; i <= n; ++i) {
            a[i].val = f[i];
            a[i].id = i;
        }
        sort(a + 1, a + 1 + n);
        string s;
        s += ‘A‘ + a[1].id - 1;
        for (int i = 2; i <= n; ++i) {
            if (a[i].val == a[i - 1].val) {
                s += "=";
            } else s += "<";
            s += ‘A‘ + a[i].id - 1;
        }
        if (mp[s]) return;
        if (s[0] == ‘C‘) {
            cout << s << endl;
            aa++;
        }
        mp[s] = true;
        return;
    }
    for (int i = 1; i <= n; ++i) {
        f[cur] = i;
        dfs(cur + 1);
    }
}
void work() {
    n = 6;
    dfs(1);
    cout << mp.size() << endl;
    cout << aa << endl;
}

dfs打表

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#define IOS ios::sync_with_stdio(false)
using namespace std;
#define inf (0x3f3f3f3f)
typedef long long int LL;

#include <iostream>
#include <sstream>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <string>
#include <iomanip>
const int maxn = 500 + 20;
void bigadd (char str1[],char str2[],char str3[]) {    //str1 + str2 = str3
    int len1=strlen(str1+1),len2=strlen(str2+1);
    char b[maxn]= {0};
    int i=len1,j=len2;
    int h=1;
    while (i>=1 && j>=1)  b[h++] = str1[i--]-‘0‘ + str2[j--]-‘0‘;
    while (i>=1)         b[h++] = str1[i--]-‘0‘;
    while (j>=1)         b[h++] = str2[j--]-‘0‘;
    for (int i=1; i<h; i++) { //h是理论越界的
        if (b[i] >= 10) {
            b[i+1]++;
            b[i] -= 10;
        }
    }
    if (!b[h]) --h;//没有进位到越界位。
    int t=h;
    for (int i=1; i<=h; i++)  str3[t--]=b[i]+‘0‘;
    str3[h+1]=‘\0‘; //一定要手动添加结束符，不然会GG
    return ;
}
char a[maxn][maxn][maxn];
char last[maxn];
char t[maxn];
void init() {
//    a[1][1] = 1.0;
    strcpy(a[1][1] + 1, "1");
//    long double last = 1.0;
    strcpy(last + 1, "1");
    for (int j = 2; j <= 52; ++j) {
//        a[j][j] = last;
        strcpy(a[j][j] + 1, last + 1);
//        printf("%s\n", a[j][j] + 1);
        for (int i = j - 1; i >= 1; --i) {
//            a[i][j] = a[i + 1][j] + a[i][j - 1];
            bigadd(a[i + 1][j], a[i][j - 1], a[i][j]);
//            printf("%s\n", a[i][j] + 1);
        }
//        last = 0;
        memset(t, 0, sizeof t);
        for (int k = j; k >= 1; --k) {
//            last += a[k][j];
            bigadd(a[k][j], t, last);
            strcpy(t + 1, last + 1);
        }
    }
}
void work() {
    int n;
    scanf("%d", &n);
    printf("%s\n", a[n + 1][n + 1] + 1);
}
int main() {
#ifdef local
    freopen("data.txt","r",stdin);
#endif
    init();
    int t;
    scanf("%d", &t);
    while (t--) work();
    return 0;
}