hdu 2510 符号三角形

打表代码:

#include <iostream>
#include <cstring>
using namespace std;

int firstLine[30]; //第一行的情况，0表示+，1表示- 
int ans[30]; //记录结果 

int count(int n) { //计算第一行为n的三角形一共有几个符号 
    return (n + 1) * n / 2;
}

void dfs(int n, int m) { //m表示当前遍历到第m个数 
    if (n >= m) {
        firstLine[m] = 0;
        dfs(n, m + 1);
        firstLine[m] = 1;
        dfs(n, m + 1);
        return;
    }
    
    int tmp[30]; //临时记录每一行的情况 
    
    int sum = 0;
    
    for (int i = 1; i <= n; i++) {
        tmp[i] = firstLine[i];
        sum += tmp[i];
    }
    
    for (int i = 2; i <= n; i++) 
        for (int j = 1; j <= n - i + 1; j++) {
            tmp[j] = tmp[j] ^ tmp[j + 1];
            sum += tmp[j];
        }
        
    if (sum == count(n) / 2)
        ans[n]++;
}


int main() {
    memset(ans, 0, sizeof(ans));
    for (int i = 1; i <= 24; i++) {
        dfs(i, 1);
        cout << ans[i] << endl;
    }
}

提交代码:

#include<iostream>
using namespace std;

int ans[25] = { 0,0,0,4,6,0,0,12,40,0,0,171,410,0,0,1896,5160,0,0,32757,59984,0,0,431095,822229 };
int main() {
    int n;
    while (cin >> n&&n)
        cout << n << " " << ans[n] << endl;
}