Best Time to Buy and Sell Stock III

class Solution {
    public int maxProfit(int[] prices) {
        if(prices == null || prices.length < 1) return 0;
        int buy1 = -prices[0], sell1 = 0, buy2 = -prices[0], sell2 = 0;
        for(int i = 1; i < prices.length; i++) {
            buy1 = Math.max(buy1, -prices[i]);
            sell1 = Math.max(sell1, buy1 + prices[i]);
            buy2 = Math.max(buy2, sell1 - prices[i]);
            sell2 = Math.max(sell2, buy2 + prices[i]);
        }
        return sell2;
    }
}

//A standard dynamic approach works as well

class Solution {
    public int maxProfit(int[] prices) {
        int N = prices.length;
        int T[][] = new int[3][N];
        
        for(int i = 1; i <= 2; i++) {
            int maxDiff = T[i-1][0] - prices[0];
            for(int j = 1; j < N; j++) {
                T[i][j] = Math.max(T[i][j-1], prices[j] + maxDiff);
                maxDiff = Math.max(maxDiff, T[i-1][j] - prices[j]);
            }
        }
        
        return T[2][N-1];
    }
}