Best Time to Buy and Sell Stock III

Say you have an array for which the ith element is the price of a given stock on day i.

Design an algorithm to find the maximum profit. You may complete at most two transactions.

Note: You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).

public class Solution {
    public int maxProfit(int[] prices) {
        //four cases: c1:buy one, c2:sell one, c3:buy two, c4:sell two
        //assume: 1.never sell one before buy one 
        //        2.never buy one before buy two
        //        3.never buy two before sell two
        //        4.never sell one before sell two
        int b1= Integer.MIN_VALUE,s1=0,b2=Integer.MIN_VALUE,s2=0;
        for(int i = 0; i < prices.length; i++){
            int p = prices[i];

            s2 = Math.max(s2,b2+p);
            b2 = Math.max(b2,s1-p);
            s1 = Math.max(s1,b1+p);
            b1 = Math.max(b1,-p);


        }
        return s2;
    }
}