Leetcode 309. Best Time to Buy and Sell Stock with Cooldown

原创于 2016-12-18 10:57:34 发布 · 185 阅读

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本文介绍了一种基于状态机的方法来实现股票买卖策略。通过定义三种状态：持有（买入）、卖出和冷却期，并利用状态转移公式进行计算，最终得出最大利润。适用于需要理解和实现股票交易策略的开发者。

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State machine graph

 
/**
 * state machine approach
 * state a(hold): hold stack, sell or rest
 * state b(sold): just sold stack can only rest
 * state c(rest): cooldown, buy or rest
 * translate to formula, 
 * stateA = max(preStateA, preStateC-prices[i])
 * stateB = preStateA+prices[i]
 * stateC = max(preStateB, preStateC)
 */ 
public class Solution {
    public int maxProfit(int[] prices) {
        if (prices.length < 2) return 0;
        
        // initialization
        int hold = -prices[0];
        int sold = Integer.MIN_VALUE;
        int rest = 0;
        
        for (int i=1; i<prices.length; i++) {
            int preHold = hold;
            hold = Math.max(hold, rest-prices[i]);
            rest = Math.max(rest, sold);
            sold = preHold + prices[i];
        }
        
        return Math.max(sold, rest);
    }
}