蓝桥杯：合并石子（区间DP+平行四边形优化）

http://lx.lanqiao.cn/problem.page?gpid=T414

题意：……

思路：很普通的区间DP，但是因为n<=1000，所以O（n^3）只能拿90分。上网查了下了解了平行四边形优化：地址。

但是看不懂。

 #include <bits/stdc++.h>
 using namespace std;
 typedef long long LL;
 const LL INF = 100000000000000000LL;
 LL dp[][], s[][];
 LL sum[];
 int main() {
     LL ans = ;
     int n; scanf("%d", &n);
     for(int i = ; i <= n; i++) scanf("%lld", &dp[i][i]), sum[i] = sum[i-] + dp[i][i], dp[i][i] = , s[i][i] = i;
     for(int len = ; len < n; len++) {
         for(int l = ; l + len <= n; l++) {
             int r = l + len;
             dp[l][r] = INF;
             for(int k = s[l][r-]; k <= s[l+][r]; k++) {
                 LL now = dp[l][k] + dp[k+][r] + sum[r] - sum[l - ];
                 if(dp[l][r] > now) dp[l][r] = now, s[l][r] = k;
             }
         }
     }
     printf("%lld\n", dp[][n]);
     return ;
 }