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Given an array of integers representing stock price on a single day, find max profit that can be earned by

**1 transaction.**

So you need to find a pair (buyDay,sellDay) where buyDay < = sellDay and it should maximize the profit.

**For example:**

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int arr[]={14, 12, 70, 15, 99, 65, 21, 90}; Max profit can be gain by buying on 1st day(0 based indexing) and sell on the 4th day. Max profit = 99-12 =87 |

## Stock Buy Sell to Maximize Profit Algorithm

Lets say we have array **arr[]** of stock prices.

We will track two variables :
lowestPriceTillThatDayand
maxProfit.

- lowestPriceTillThatDay will be initialise to arr[0].
- Iterate over stock price array arr[]
- If
current element is greater than
lowestPriceTillThatDay
- calculate
**profit**. - If
profit is greater than
**maxProfit**then update the maxProfit.

- calculate
- If
current element is lesser than
lowestPriceTillThatDay
- update lowestPriceTillThatDay with current element.

- We will get maxProfit in the end.

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public static int calculateMaxProfit(int[] arr) { int lowestPriceTillThatDay = arr[0]; int maxProfit = Integer.MIN_VALUE; for (int i = 0; i < arr.length; i++) { int profit = 0; if (arr[i] > lowestPriceTillThatDay) { profit = arr[i] - lowestPriceTillThatDay; if (profit > maxProfit) { maxProfit = profit; } } else { lowestPriceTillThatDay = arr[i]; } } return maxProfit; } |

## Java Program for Stock Buy Sell to Maximize Profit

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package org.arpit.java2blog; public class StockBuySellMain { public static void main(String[] args) { int arr[] = { 14, 12, 70, 15, 99, 65, 21, 90 }; System.out.println("Maximum profit :" + calculateMaxProfit(arr)); } public static int calculateMaxProfit(int[] arr) { int lowestPriceTillThatDay = arr[0]; int maxProfit = Integer.MIN_VALUE; for (int i = 0; i < arr.length; i++) { int profit = 0; if (arr[i] > lowestPriceTillThatDay) { profit = arr[i] - lowestPriceTillThatDay; if (profit > maxProfit) { maxProfit = profit; } } else { lowestPriceTillThatDay = arr[i]; } } return maxProfit; } } |

When you run above program, you will get below output:

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Maximum profit :87 |

That’s all about Stock Buy Sell to Maximize Profit.