From 7e96b3aee6f95276fb0a6b3fb270c499cbcbc15d Mon Sep 17 00:00:00 2001 From: Akshit Bansal <155195875+akshitbansal2005@users.noreply.github.com> Date: Wed, 2 Oct 2024 15:14:48 +0530 Subject: [PATCH 1/4] Update BestTimeToBuyAndSellStock.java MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Code Analysis Let's break down the code and examine it for potential issues: Kadane's Algorithm Comment: The comment states that this uses "Kadane's algorithm." Kadane's algorithm typically applies to problems related to finding the maximum sum of subarrays (like the maximum subarray sum problem). This code does not implement Kadane’s algorithm but instead is a form of "single-pass" algorithm for the maximum profit in stock prices. The comment is misleading and should be corrected. Edge Case Handling: The code handles the case where the input array is empty (prices.length == 0). This is good, but we could simplify the check or add other edge cases such as prices containing only one element, where no transactions are possible. Variable Naming: The variable names min and max are vague. More descriptive names such as minPrice and maxProfit would improve code readability. Performance Consideration: The algorithm is optimal and runs in O(n) time, which is appropriate for this problem. However, clarity could be improved in the loop's structure and comments. Logical Flow: The current logic is sound for calculating the maximum profit in a single transaction, but the logic could be made more intuitive by reorganizing it slightly to better separate the identification of the minimum price and the calculation of the profit. Improvements Comment Clarification: Update the misleading comment about Kadane's algorithm. Edge Case Enhancements: Ensure the function is handling cases such as arrays of length 1 or very large values. Naming: Use more descriptive variable names. Code Structuring: The current structure works fine, but adding comments for readability and restructuring some checks can make the logic clearer. --- leetcode/array/BestTimeToBuyAndSellStock.java | 44 +++++++------------ 1 file changed, 17 insertions(+), 27 deletions(-) diff --git a/leetcode/array/BestTimeToBuyAndSellStock.java b/leetcode/array/BestTimeToBuyAndSellStock.java index 356bd0d7..7b37492d 100644 --- a/leetcode/array/BestTimeToBuyAndSellStock.java +++ b/leetcode/array/BestTimeToBuyAndSellStock.java @@ -1,36 +1,26 @@ -// Say you have an array for which the ith element is the price of a given stock on day i. - -// If you were only permitted to complete at most one transaction (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit. - -// Example 1: -// Input: [7, 1, 5, 3, 6, 4] -// Output: 5 - -// max. difference = 6-1 = 5 (not 7-1 = 6, as selling price needs to be larger than buying price) -// Example 2: -// Input: [7, 6, 4, 3, 1] -// Output: 0 - -// In this case, no transaction is done, i.e. max profit = 0. - public class BestTimeToBuyAndSellStock { + public int maxProfit(int[] prices) { - //Kadane's algorithm - if(prices.length == 0) { + // Return 0 if there are no prices or only one price (no transaction possible) + if (prices == null || prices.length < 2) { return 0; } - int min = prices[0]; - int max = 0; - - for(int i = 1; i < prices.length; i++) { - if(prices[i] > min) { - max = Math.max(max, prices[i] - min); - } else { - min = prices[i]; - } + int minPrice = prices[0]; // Initialize with the first price + int maxProfit = 0; // No profit made at the start + + // Iterate over the prices starting from the second day + for (int i = 1; i < prices.length; i++) { + // Calculate profit by selling at current price and buying at the minimum price + int currentProfit = prices[i] - minPrice; + + // Update the maximum profit if current profit is higher + maxProfit = Math.max(maxProfit, currentProfit); + + // Update the minimum price if current price is lower + minPrice = Math.min(minPrice, prices[i]); } - return max; + return maxProfit; } } From 1ab9649efb520f832373ed40cdc051e333c2bf07 Mon Sep 17 00:00:00 2001 From: Akshit Bansal <155195875+akshitbansal2005@users.noreply.github.com> Date: Wed, 2 Oct 2024 15:34:33 +0530 Subject: [PATCH 2/4] Update AddTwoNumbers.java MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Issues Identified Initial Value of sum: The variable sum is initialized to 0, but within the loop, the first operation is sum /= 10, which effectively nullifies this initialization. This line is meant to handle the carry between digits but can be misleading when done at the start of each iteration. Carry Propagation: The carry is correctly handled by dividing sum by 10, but the logic for handling the carry could be clearer. Specifically, the carry check is only done at the end (if(sum / 10 == 1)), which is correct for cases where the final sum is more than one digit, but this can be improved for clarity and correctness. Variable Naming: The variable names current1, current2, and currentHead can be made more descriptive. For instance, current1 and current2 can be renamed to node1 and node2 for clarity. Loop Structure: The loop will terminate when both current1 and current2 are null, but there’s a redundant check at the end for the carry (sum / 10 == 1). This check could be simplified by ensuring the carry is handled within the loop itself. Edge Case: If both input lists are null, the function should return null, but the current implementation returns a dummy node with value 0. We can optimize this by removing the dummy node when not necessary. --- company/amazon/AddTwoNumbers.java | 47 ++++++++++++++++--------------- 1 file changed, 24 insertions(+), 23 deletions(-) diff --git a/company/amazon/AddTwoNumbers.java b/company/amazon/AddTwoNumbers.java index 864fb6ca..2088e53e 100644 --- a/company/amazon/AddTwoNumbers.java +++ b/company/amazon/AddTwoNumbers.java @@ -15,35 +15,36 @@ */ public class AddTwoNumbers { public ListNode addTwoNumbers(ListNode l1, ListNode l2) { - ListNode current1 = l1; - ListNode current2 = l2; + ListNode dummyHead = new ListNode(0); // Dummy node to simplify the result list creation + ListNode current = dummyHead; // Pointer for traversing the result list + int carry = 0; // Variable to track the carry - ListNode head = new ListNode(0); - ListNode currentHead = head; - - int sum = 0; - - while(current1 != null || current2 != null) { - sum /= 10; + // Traverse both lists until both are null and there's no carry left + while (l1 != null || l2 != null || carry != 0) { + int sum = carry; // Start with the carry from the previous addition - if(current1 != null) { - sum += current1.val; - current1 = current1.next; + // Add value from the first list if available + if (l1 != null) { + sum += l1.val; + l1 = l1.next; } - if(current2 != null) { - sum += current2.val; - current2 = current2.next; + // Add value from the second list if available + if (l2 != null) { + sum += l2.val; + l2 = l2.next; } - - currentHead.next = new ListNode(sum % 10); - currentHead = currentHead.next; - } - - if(sum / 10 == 1) { - currentHead.next = new ListNode(1); + + // Compute the new carry (either 1 or 0) for the next iteration + carry = sum / 10; + + // Create a new node with the digit and attach it to the result list + current.next = new ListNode(sum % 10); + current = current.next; } - return head.next; + // Return the result list, skipping the dummy head + return dummyHead.next; } } + From 2f3473bcf1a182cabf397b7a54cca6d32635a803 Mon Sep 17 00:00:00 2001 From: Akshit Bansal <155195875+akshitbansal2005@users.noreply.github.com> Date: Thu, 3 Oct 2024 13:39:18 +0530 Subject: [PATCH 3/4] Update BestTimeToBuyAndSellStock.java Analysis of the Code Null and Length Check: The check for null or length less than 2 is appropriate and necessary to avoid unnecessary computations or errors. Variable Naming: Variable names like minPrice and maxProfit are clear and descriptive. However, currentProfit might be more intuitively named as potentialProfit to clarify that it represents the profit based on the current selling price. Loop Starting Point: The loop starts at index 1, which is correct since it initializes minPrice with the first element. However, it could be more explicitly documented. Commenting: Comments are generally clear, but a few additional comments explaining the logic could enhance understanding. Use of Math.max and Math.min: The use of these methods is efficient and clear. However, you can provide an explanation that these are used to track the best scenarios. --- leetcode/array/BestTimeToBuyAndSellStock.java | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/leetcode/array/BestTimeToBuyAndSellStock.java b/leetcode/array/BestTimeToBuyAndSellStock.java index 7b37492d..95592103 100644 --- a/leetcode/array/BestTimeToBuyAndSellStock.java +++ b/leetcode/array/BestTimeToBuyAndSellStock.java @@ -1,5 +1,5 @@ public class BestTimeToBuyAndSellStock { - + public int maxProfit(int[] prices) { // Return 0 if there are no prices or only one price (no transaction possible) if (prices == null || prices.length < 2) { @@ -11,16 +11,16 @@ public int maxProfit(int[] prices) { // Iterate over the prices starting from the second day for (int i = 1; i < prices.length; i++) { - // Calculate profit by selling at current price and buying at the minimum price - int currentProfit = prices[i] - minPrice; + // Calculate potential profit by selling at the current price and buying at the minimum price + int potentialProfit = prices[i] - minPrice; - // Update the maximum profit if current profit is higher - maxProfit = Math.max(maxProfit, currentProfit); + // Update the maximum profit if the potential profit is higher + maxProfit = Math.max(maxProfit, potentialProfit); - // Update the minimum price if current price is lower + // Update the minimum price if the current price is lower minPrice = Math.min(minPrice, prices[i]); } - return maxProfit; + return maxProfit; // Return the maximum profit found } } From 3ee0bb160cc8e2719b5f16531f41def5649b0241 Mon Sep 17 00:00:00 2001 From: Akshit Bansal <155195875+akshitbansal2005@users.noreply.github.com> Date: Thu, 3 Oct 2024 13:46:19 +0530 Subject: [PATCH 4/4] Update ContainsDuplicatesII.java MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Code Analysis Functionality: The logic of using a HashMap to store the indices of the elements is appropriate and efficient. This allows for constant time complexity for lookups and updates. Correctness: The code correctly checks for the existence of nearby duplicates by verifying if the current number has been seen before and if the difference in their indices is less than or equal to k. This is the correct approach to solving the problem. Clarity and Readability: The variable names (indexMap and currentValue) are descriptive and make the code easier to understand. The comments effectively explain what each part of the code is doing, which is helpful for readability. Edge Cases: The code should handle edge cases, such as: An empty array (nums). An array with only one element. Cases where k is 0 (in which case duplicates must be at the same index, which isn’t possible). --- leetcode/array/ContainsDuplicatesII.java | 38 ++++++++++++++++++------ 1 file changed, 29 insertions(+), 9 deletions(-) diff --git a/leetcode/array/ContainsDuplicatesII.java b/leetcode/array/ContainsDuplicatesII.java index 81240ea2..a6ee2a7c 100644 --- a/leetcode/array/ContainsDuplicatesII.java +++ b/leetcode/array/ContainsDuplicatesII.java @@ -1,18 +1,38 @@ //Given an array of integers and an integer k, find out whether there are two distinct indices i and //j in the array such that nums[i] = nums[j] and the absolute difference between i and j is at most k. +import java.util.Map; +import java.util.HashMap; + class ContainsDuplicatesII { + /** + * Check if there are duplicates within a given distance k. + * + * @param nums the array of integers + * @param k the maximum distance + * @return true if duplicates exist within distance k, false otherwise + */ public boolean containsNearbyDuplicate(int[] nums, int k) { - HashMap map = new HashMap(); - for(int i = 0; i < nums.length; i++) { - int current = nums[i]; - if(map.containsKey(current) && i - map.get(current) <= k) { - return true; - } else { - map.put(current, i); + // Return false if nums is null or has fewer than 2 elements + if (nums == null || nums.length < 2 || k < 0) { + return false; + } + + // Use a Map to store the most recent index of each value + Map indexMap = new HashMap<>(); + + for (int i = 0; i < nums.length; i++) { + int currentValue = nums[i]; + + // Check if the current value has been seen before and within the allowed distance + if (indexMap.containsKey(currentValue) && (i - indexMap.get(currentValue) <= k)) { + return true; // Found a nearby duplicate } + + // Update the index of the current value + indexMap.put(currentValue, i); } - - return false; + + return false; // No nearby duplicates found } }