maxRange.js

// Write a function that returns the maximum returns
// given a sequence of prices.

const stockPrices1 = [10, 7, 5, 8, 11, 9];
const stockPrices2 = [3, 7, 5, 13, 1, 8];
const stockPrices3 = [88, 4, 12, 3, 2, 1];
const stockPrices4 = [12, 16, 3, 2, 8, 7];

function getMaxProfit(prices) {
    //Set the inial range
    var maxReturns = prices[1] - prices[0];
  
    for(var i = 0; i < prices.length -1; i++) {
        for(var j = i+1; j < prices.length; j++) {
            
            //i is the buying price and j is the selling price
            var range = prices[j] - prices[i];
            
            //Check if the range is greater than the current range
            if(range > maxReturns){
                maxReturns = range;
            }
        }
    }
  
  console.log(maxReturns);
}

getMaxProfit(stockPrices1); // 6
getMaxProfit(stockPrices2); // 10
getMaxProfit(stockPrices3); // 8
getMaxProfit(stockPrices4); // 6

//Since we are trying to find the gains from buying and selling 'stock' you have to buy first and then sell, this is why j = i + 1. Then you can just compare the numbers. 
//The runtime though for this is O(n^2) since we are looking at a starting buying price (n-1) and looking at all possible selling prices (n-1)


function getMaxProfitInNTime(prices) {
    //Set the default price
    var maxReturns = prices[1] - prices[0];
    
    //Get the lowest buy price
    var minPrice = prices[0];
  
    for(var i = 1; i < prices.length; i++) {
        
        //Find the range of the current price and the minimum (so far) price
        var range = prices[i] - minPrice;
        
        //Check dat $$$
        if(range > maxReturns)
            maxReturns = range;
            
        //Update the lowest price we've seen
        if(minPrice > prices[i])
            minPrice = prices[i];
        
    }
  
  console.log(maxReturns);
}

getMaxProfitInNTime(stockPrices1); // 6
getMaxProfitInNTime(stockPrices2); // 10
getMaxProfitInNTime(stockPrices3); // 8
getMaxProfitInNTime(stockPrices4); // 6

//In this we get the profit in O(n) cause after doing it in O(n^2) I remember doing a problem similar to this before (that I think you sent me lol)
//Basically set the inital values of the range and minimum price
//Start the loop at 1 (since we are using the index as our selling price) and check if the range is greater than the current max range
//If so, update the max range and after check if the minimum price is the lowest we've seen
//We have to check the range first before we update the minimum price since i-i would equal 0