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BuyAndSellStockIII.java
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BuyAndSellStockIII.java
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package Leetcode;
/**
* @author kalpak
*
* 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
* (i.e., you must sell the stock before you buy again).
*
*
* Example 1:
* Input: prices = [3,3,5,0,0,3,1,4]
* Output: 6
* Explanation: Buy on day 4 (price = 0) and sell on day 6 (price = 3), profit = 3-0 = 3.
* Then buy on day 7 (price = 1) and sell on day 8 (price = 4), profit = 4-1 = 3.
*
* Example 2:
* Input: prices = [1,2,3,4,5]
* Output: 4
* Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5), profit = 5-1 = 4.
* Note that you cannot buy on day 1, buy on day 2 and sell them later,
* as you are engaging multiple transactions at the same time. You must sell before buying again.
*
* Example 3:
* Input: prices = [7,6,4,3,1]
* Output: 0
* Explanation: In this case, no transaction is done, i.e. max profit = 0.
*
* Example 4:
* Input: prices = [1]
* Output: 0
*
* Constraints:
* 1 <= prices.length <= 10^5
* 0 <= prices[i] <= 10^5
*/
public class BuyAndSellStockIII {
public static int maxProfit(int[] prices) {
if(prices.length == 0 || prices == null)
return 0;
int buy1 = Integer.MAX_VALUE;
int profit1 = Integer.MIN_VALUE;
int buy2 = Integer.MAX_VALUE;
int profit2 = Integer.MIN_VALUE;
for(int i = 0; i < prices.length; i++) {
buy1 = Math.min(buy1, prices[i]);
profit1 = Math.max(profit1, prices[i] - buy1);
buy2 = Math.min(buy2, prices[i] - profit1);
profit2 = Math.max(profit2, prices[i] - buy2);
}
return profit2;
}
public static int maxProfitUsingDivideAndConquerAndDP(int[] prices) {
if(prices.length == 0 || prices == null) {
return 0;
}
int[] left = new int[prices.length]; // highest profit in 0 ... i
int[] right = new int[prices.length]; // highest profit in i ... n - 1
// DP from left to right
int min = prices[0];
for (int i = 1; i < prices.length; i++) {
min = Math.min(min, prices[i]);
left[i] = Math.max(left[i - 1], prices[i] - min);
}
// DP from right to left
int max = prices[prices.length - 1];
for (int i = prices.length - 2; i >= 0; i--) {
max = Math.max(max, prices[i]);
right[i] = Math.max(right[i + 1], max - prices[i]);
}
int profit = 0;
for (int i = 0; i < prices.length; i++) {
profit = Math.max(profit, left[i] + right[i]);
}
return profit;
}
public static void main(String[] args) {
int[] prices = new int[]{3,3,5,0,0,3,1,4};
System.out.println(maxProfit(prices));
System.out.println(maxProfitUsingDivideAndConquerAndDP(prices));
}
}