題目鏈接：https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/description/
題目標簽：Array，DP
此題與123. Best Time to Buy and Sell Stock III 相比，交易數(shù)量由2個上升至K個，基本思路還是一樣，只是現(xiàn)在要同時更新k個buy，k個sell。
Java代碼：

class Solution {
    public int maxProfit(int k, int[] prices) {
        int len = prices.length;
        if(len==0 || k==0){
            return 0;
        }
        if (k>= len/2){
            return quickSolve(prices);
        }
        
        int[][] statue = new int[k][len];
        // initialize statue[0]
        int buy = -prices[0];
        for (int i=1; i<len; i++){
            statue[0][i] = Math.max(statue[0][i-1], prices[i] + buy);
            buy = Math.max(buy, -prices[i]);
        }
        // fullfill statue
        for (int i=1; i<k; i++){
            buy = -prices[0];
            for (int j=1; j<len; j++){
                statue[i][j] = Math.max(statue[i][j-1], prices[j] + buy);
                buy = Math.max(buy, statue[i-1][j-1]-prices[j]);
            }
        }
        return statue[k-1][len-1];
    }
    
    private int quickSolve(int[] prices){
        int len = prices.length;
        int res = 0;
        for(int i=1; i<len; i++){
            int p1 = prices[i-1];
            int p2 = prices[i];
            if(p2>p1){
                res += p2-p1;
            }
        }
        return res;
    }
}

Edge case:

k = 0
prices = []
k>=prices.length/2