[LeetCode]121 Best Time to Buy and Sell Stock

public class Solution {
public int maxProfit(int[] prices)
{
// Solution A:
return maxProfit_DP(prices);

// Solution B:
// return maxProfit_Binary(prices);
}

/////////////////////////////
// Solution A: DP
//
// global: 全局最优
// local: 在今天卖出的最优
//  在i-1 天卖出 的是 local
//  在i天卖出的是 max(local + (price[i] - price[i - 1]), 0)
private int maxProfit_DP(int[] prices)
{
if (prices == null || prices.length <= 1)
return 0;

int local = 0;
int global = 0;
for (int i = 1 ; i < prices.length ; i ++)
{
local = Math.max(local + prices[i] - prices[i - 1] , 0);
global = Math.max(local, global);
}
return global;
}

/////////////////////////////
// Solution A: Binary
//
public int maxProfit_Binary(int[] prices)
{
if (prices == null || prices.length == 0)
return 0; // Invalid input.

Values value = calc(prices, 0, prices.length - 1);
return value.pro;
}

private Values calc(int[] prices, int low, int high)
{
if (low == high)
{
return new Values(prices[low], prices[low], 0);
}

int mid = (low + high) / 2;

Values left = calc(prices, low, mid);
Values right = calc(prices, mid + 1, high);

int max = Math.max(left.max, right.max);
int min = Math.min(left.min, right.min);
int pro = Math.max(left.pro, right.pro);
pro = Math.max(pro, right.max - left.min);
return new Values(max, min, pro);
}

private static class Values
{
Values(int max, int min, int pro)
{
this.max = max;
this.min = min;
this.pro = pro;
}

int max;
int min;
int pro;
}
}