Luogu1063 能量项链 （区间DP）

惊恐地发现自己连区间DP都会错2333

#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("\n\n----------\n\n")
#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;

const int N = 1007;
int a[N], f[N][N];

int main(){
	//FileOpen();

	int n;
    io >> n;
    R(i,1,n){
    	io >> a[i];
    	a[i + n] = a[i];
    }

    int ans = 0;
    R(len,2,n){
    	R(l,1,n << 1){
    		int r = l + len - 1;
    		if(r > (n << 1)) continue;
    		R(k, l + 1, r){
    			f[l][r] = Max(f[l][r], f[l][k - 1] + f[k][r] + a[l] * a[k] * a[r + 1]);
    			ans = Max(ans, f[l][r]);
    		//1	printf("f %d %d :%d\n", l, r, f[l][r]);
    		}
    	}
    }

    printf("%d", ans);

	return 0;
}