Max Profit

maxProfitCalculator.php

<?php

// https://coderbyte.com/algorithm/stock-maximum-profit

function StockPicker($arr) {
    $buyPrice = 0;
    $sellPrice = 0;
    $maxProfit = -1;
    
    $changeBuyIndex = true;
    
    for($i = 0; $i < count($arr) - 1; $i++) {
        if($changeBuyIndex) {
            $buyPrice = $arr[$i];
        }
        // echo "Buy price: " . $buyPrice . ' ';
        
        $sellPrice = $arr[$i+1];
        // echo "Sell price: " . $sellPrice . ' ';
        
        if($buyPrice < $sellPrice) {
            $changeBuyIndex = false;
            
            $currentProfit = $sellPrice - $buyPrice;
            
            if($maxProfit < $currentProfit)
                $maxProfit = $currentProfit;
        } else {
            $changeBuyIndex = true;
        }
        
        // echo "Max profit: " . $maxProfit;
        
        // echo "\n";
    }
    
    return $maxProfit;
}

echo StockPicker([44, 30, 24, 32, 40, 20, 40, 38, 15]);