【动态规划】买卖股票的最佳时机Ⅳ

题目链接：https://leetcode.cn/problems/best-time-to-buy-and-sell-stock-iv/description/

class Solution {
public:
const int INF = 0x3f3f3f3f;
int maxProfit(int k, vector<int>& prices)
{
/*时空复杂度O(nk)*/
int n = prices.size();
k = min(k, n / 2);
// 1. 创建dp表
vector<vector<int>> f(n, vector<int>(k + 1, –INF));
auto g = f;
// 2. 初始化
f[0][0] = –prices[0], g[0][0] = 0;
// 3. 填表
for (int i = 1; i < n; ++i)
for (int j = 0; j <= k; ++j)
{
f[i][j] = max(f[i – 1][j], g[i – 1][j] – prices[i]);
g[i][j] = g[i – 1][j];
if (j >= 1) g[i][j] = max(g[i – 1][j], f[i – 1][j – 1] + prices[i]);
}
// 4. 返回值
int ret = 0;
for (int j = 0; j <= k; ++j)
ret = max(ret, g[n – 1][j]);
return ret;
}
};