3052 [USACO12MAR]摩天大楼里的奶牛Cows in a Skyscraper （状压DP，IDA*）

状压DP:

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define R(a,b,c) for(register int  a = (b); a <= (c); ++ a)
#define nR(a,b,c) for(register int  a = (b); a >= (c); -- a)
#define Max(a,b) ((a) > (b) ? (a) : (b))
#define Min(a,b) ((a) < (b) ? (a) : (b))
#define Fill(a,b) memset(a, b, sizeof(a))
#define Abs(a) ((a) < 0 ? -(a) : (a))
#define Swap(a,b) a^=b^=a^=b
#define ll long long

#define ON_DEBUG

#ifdef ON_DEBUG

#define D_e_Line printf("

----------

")
#define D_e(x)  cout << #x << " = " << x << endl
#define Pause() system("pause")
#define FileOpen() freopen("in.txt","r",stdin);

#else

#define D_e_Line ;
#define D_e(x)  ;
#define Pause() ;
#define FileOpen() ;

#endif

struct ios{
    template<typename ATP>ios& operator >> (ATP &x){
        x = 0; int f = 1; char c;
        for(c = getchar(); c < '0' || c > '9'; c = getchar()) if(c == '-')  f = -1;
        while(c >= '0' && c <= '9') x = x * 10 + (c ^ '0'), c = getchar();
        x*= f;
        return *this;
    }
}io;
using namespace std;

int a[23], f[(1 << 18) + 7], g[(1 << 18) + 7];

int main(){
    int n, V;
    io >> n >> V;

    R(i,1,n){
    	io >> a[i];
    }
	
	int M = (1 << n) - 1;
	R(s,1,M) f[s] = 2147483647;
    f[0] = 1;
    g[0] = V;

    R(s,0,M){
        R(i,1,n){
            if(s & (1 << (i - 1))) continue;
            if(g[s] >= a[i] && f[s | (1 << (i - 1))] >= f[s]){
                f[s | (1 << (i - 1))] = f[s];
                g[s | (1 << (i - 1))] = Max(g[s | (1 << (i - 1))], g[s] - a[i]);
            }
            else if(g[s] < a[i] && f[s | (1 << (i - 1))] >= f[s] + 1){
                f[s | (1 << (i - 1))] = f[s] + 1;
                g[s | (1 << (i - 1))] = Max(g[s | (1 << (i - 1))], V - a[i]);
            }
        }
    }

    printf("%d", f[M]);

    return 0;
}

IDA*:

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define R(a,b,c) for(register int  a = (b); a <= (c); ++ a)
#define nR(a,b,c) for(register int  a = (b); a >= (c); -- a)
#define Max(a,b) ((a) > (b) ? (a) : (b))
#define Min(a,b) ((a) < (b) ? (a) : (b))
#define Fill(a,b) memset(a, b, sizeof(a))
#define Abs(a) ((a) < 0 ? -(a) : (a))
#define Swap(a,b) a^=b^=a^=b
#define ll long long

#define ON_DEBUG

#ifdef ON_DEBUG

#define D_e_Line printf("

----------

")
#define D_e(x)  cout << #x << " = " << x << endl
#define Pause() system("pause")
#define FileOpen() freopen("in.txt","r",stdin);

#else

#define D_e_Line ;
#define D_e(x)  ;
#define Pause() ;
#define FileOpen() ;

#endif

struct ios{
    template<typename ATP>ios& operator >> (ATP &x){
        x = 0; int f = 1; char c;
        for(c = getchar(); c < '0' || c > '9'; c = getchar()) if(c == '-')  f = -1;
        while(c >= '0' && c <= '9') x = x * 10 + (c ^ '0'), c = getchar();
        x*= f;
        return *this;
    }
}io;
using namespace std;

int n, V;
int a[19], w[19];

inline bool DFS(int x, int dep){
	int minn = Min(x, dep);
	R(i,1,minn){
		if(w[i] + a[x] <= V){
			w[i] += a[x];
			if(x == n) return 1;
			if(DFS(x + 1, dep)) return 1;
			w[i] -= a[x];
		}
	}
	return 0;
}
int main(){
    io >> n >> V;
    R(i,1,n){
    	io >> a[i];
    }
    R(i,1,n){
        Fill(w, 0);
        if(DFS(1, i)){
            printf("%d", i);
            return 0;
        }
    }
    
    return 0;
}