leetcode1140 Stone Game II

思路：

dp，用记忆化搜索比较好实现。

实现：

 class Solution
 {
 public:
     int dfs(vector<int>& sum, int cur, int M, vector<vector<int>>& dp)
     {
         int n = sum.size();
         if (n - cur <=  * M) return sum[n - ] - sum[cur];
         if (dp[cur][M] != -) return dp[cur][M];
         int ans = INT_MIN;
         for (int i = ; i <= min( * M, n - cur); i++)
         {
             int tmp = dfs(sum, cur + i, max(M, i), dp);
             ans = max(ans, sum[cur + i - ] - sum[cur] + sum[n - ] - sum[cur + i - ] - tmp);
         }
         return dp[cur][M] = ans;
     }
     int stoneGameII(vector<int>& piles)
     {
         int n = piles.size();
         vector<int> sum(n + , );
         vector<vector<int>> dp(n + , vector<int>(n + , -));
         for (int i = ; i <= n; i++) sum[i] = sum[i - ] + piles[i - ];
         int res = dfs(sum, , , dp);
         return res;
     }
 }