USACO08NOV Mixed Up Cows

题目传送门

最近做了好多“奶牛题”

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比较简单的状压DP

直接记录集合无法转移，还要再加上一维，表示末尾的牛的编号

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
using namespace std;
#define LL long long
LL read() {
    LL k = 0, f = 1; char c = getchar();
    while(c < '0' || c > '9') {
        if(c == '-') f = -1;
        c = getchar();
    }
    while(c >= '0' && c <= '9')
      k = k * 10 + c - 48, c = getchar();
    return k * f;
}
LL a[20], f[1 << 16][20];
int main() {
    int n = read(), k = read();
    for(int i = 0; i < n; ++i) a[i] = read(), f[1 << i][i] = 1;
    for(int s = 1; s <= (1 << n) - 1; ++s)
        for(int i = 0; i < n; ++i)
            if((1 << i) & s)
                for(int j = 0; j < n; ++j)
                    if(i != j && ((1 << j) & s) && abs(a[i] - a[j]) > k) f[s][i] += f[s ^ (1 << i)][j];
    LL ans = 0;
    for(int i = 0; i < n; ++i) 
        ans += f[(1 << n) - 1][i];
    cout << ans;
    return 0;
}