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121. Best Time to Buy and Sell Stock (#100)
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/*
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121. Best Time to Buy and Sell Stock
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https://leetcode.com/problems/best-time-to-buy-and-sell-stock/description/
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Problem:
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You are given an array prices where prices[i] is the price of a given stock on the ith day.
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You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.
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Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.
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Example 1:
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Input: prices = [7,1,5,3,6,4]
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Output: 5
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Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
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Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.
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Example 2:
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Input: prices = [7,6,4,3,1]
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Output: 0
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Explanation: In this case, no transactions are done and the max profit = 0.
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Constraints:
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1 <= prices.length <= 10^5
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0 <= prices[i] <= 10^4
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*/
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/*
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Approach:
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We will use a Two pointers strategy (Left and Right pointers).
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The first will start pointing to the first element, and the right to the second position of array.
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The Left is to buy stock and Right is to sell stock
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We initialize our maxProfitValue as 0.
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Now we will start our while loop, and we will run till our
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Right pointer less than the array's length.
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For Example:
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prices=[7,1,5,3,6,4]
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Note:
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prices[left] --> buy stock
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prices[right] --> sell stock
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We will check the price at the right and left pointer
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step 1:
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price[left]=7 price[right]=1 profit=-6
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here, price[left] is greater than price[right], so we will move the left pointer to the right position
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and increment our right pointer by 1. We always want our left point to be the minimum.
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step 2:
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price[left]=1 price[right]=5 profit=4
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here, price[left] is less than price[right], which means we will get profit,
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so we will update our maxProfitValue and move our right pointer alone
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step 3:
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price[left]=1 price[right]=3 profit=2
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here, price[left] is less than price[right], we will get profit, so we will compare the maxProfitValue with the current profit.
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We will update our maxProfitValue and move our right pointer alone
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step 4:
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price[left]=1 price[right]=6 profit=5
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same logic as above
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step 5:
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price[left]=1 price[right]=4 profit=3
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same logic as above
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*/
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const maxProfit = (prices) => {
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let left = 0; // Buy
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let right = 1; // sell
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let maxProfitValue = 0;
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while (right < prices.length) {
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if (prices[left] < prices[right]) {
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let profit = prices[right] - prices[left]; // our current profit
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maxProfitValue = Math.max(maxProfitValue, profit);
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} else {
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left = right;
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}
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right++;
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}
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return maxProfitValue;
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};
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module.exports.maxProfit = maxProfit;
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const assert = require("assert");
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const maxProfitEqual = require("../../../LeetcodeProblems/Algorithms/easy/Best_Time_to_buy_and_sell_stock").maxProfit;
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function test() {
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assert.deepEqual(
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maxProfit([7,1,5,3,6,4]),
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5
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);
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assert.deepEqual(
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maxProfit([7,6,4,3,1]),
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0
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);
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}
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module.exports.test = test;

‎README.md

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@@ -72,6 +72,7 @@ The solutions are located under `/LeetcodeProblems`. Each problem has a test fil
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| [Gas Station](/LeetcodeProblems/Algorithms/medium/GasStation/index.js) | Medium | https://leetcode.com/problems/gas-station/description/ |
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| [K Closest Points to Origin](/LeetcodeProblems/Algorithms/medium/K_Closest_Points_to_Origin.js/) | Medium | https://leetcode.com/problems/k-closest-points-to-origin/
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| [BestTimeToBuy](LeetcodeProblems/Algorithms/easy/Best_Time_To_Buy_And_Sell_Stock_II.js) | Medium | https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii |
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| [Best Time to Buy and Sell Stock](/LeetcodeProblems/Algorithms/easy/Best_Time_to_buy_and_sell_stock.js) | Easy | https://leetcode.com/problems/best-time-to-buy-and-sell-stock/
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| [Flood Fill ](/LeetcodeProblems/Algorithms/easy/Flood_Fill.js) | Easy | https://leetcode.com/problems/flood-fill/ |
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| [Implement stack using queues ](/LeetcodeProblems/Algorithms/easy/Implement_stack_using_queues.js) | Easy | https://leetcode.com/problems/implement-stack-using-queues/ |
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| [Number of Segments in a String ](/LeetcodeProblems/Algorithms/easy/Number_of_Segments_in_a_String.js) | Easy | https://leetcode.com/problems/number-of-segments-in-a-string/ |

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