2006年提高组 能量项链 (区间dp)

提交Link: http://wikioi.com/problem/1154/
状态:dp[i][j] 表示第【i,j】的最优结果
状态转移: dp[i][j] = max（dp[i][k]+dp[k+1][j]+cost)

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

#define MAXN    111
#define INF     0x7fffffff

typedef struct NODE_ {
        int  l, r;
}NODE;

NODE val[MAXN], ori[MAXN];
int  dp[MAXN][MAXN], tmp[MAXN];

void conversion(const int &idx, const int &n)
{
        int index(0);
        for(int i = idx; i < n; i ++) {
                val[index ++] = ori[i];
        }
        for(int i = 0; i < idx; i ++) {
                val[index ++] = ori[i];
        }
}

int  dfs(const int &l, const int &r)
{
        if( l >= r ) {
                return 0;
        }
        if( -1 != dp[l][r] ) {
                return dp[l][r];
        }
        int  rst(0);
        for(int k = l; k < r; k ++) {
                rst = max(rst, dfs(l, k)+dfs(k+1, r)+val[l].l*val[k].r*val[r].r);
        }
        return dp[l][r] = rst;
}

int main(int argc, char const *argv[])
{
#ifndef ONLINE_JUDGE
        freopen("test.in", "r", stdin);
#endif
        int  n, idx, rst;
        scanf("%d", &n);
        for(int i = 0; i < n; i ++) {
                scanf("%d", &tmp[i]);
        }
        rst = 0; idx = 0;
        for(int i = 0; i < n-1; i ++) {
                ori[idx].l = tmp[i]; ori[idx ++].r = tmp[i+1];
        }
        ori[idx].l = tmp[n-1]; ori[idx].r = tmp[0];
        for(int i = 0; i < n; i ++) {
                conversion(i, n); memset(dp, -1, sizeof(dp)); rst = max(rst, dfs(0, n-1));
        }
        printf("%d\n", rst);
        return 0;
}