Today, we will discuss a case of debugging when solving coding test problems using Swift.
To solve algorithmic problems, it is essential to go through the processes of understanding the problem, designing, implementing, and debugging.
Here, we will set up a simple algorithmic problem and look at various issues that may arise during the solution process and how to resolve them through debugging.
Problem Description: Two Sum
Given an integer array nums and an integer target,
the problem is to return the indices of the two numbers such that they add up to target.
There is exactly one solution for each input, and you may not use the same element twice.
The constraints are that the length of the nums array is between 2 and 10,000, and each element is between -10,000 and 10,000.
Input Example
nums = [2, 7, 11, 15], target = 9
Output Example
[0, 1] (2 + 7 = 9)
Problem Solving Process
Step 1: Problem Analysis
The given problem requires finding two numbers, so we could use a nested loop, but
for efficiency, using a hashmap will be a better approach.
Using a hashmap allows us to reduce the time complexity to O(n).
Step 2: Algorithm Design
The problem can be solved with the following steps:
- Initialize an empty hashmap.
- Iterate through the array to calculate the current value and the target value.
- Add the current value as the key and the index as the value to the hashmap.
- If the target value is in the hashmap, return its index.
Step 3: Code Implementation
Below is the code implemented in Swift:
func twoSum(_ nums: [Int], _ target: Int) -> [Int] {
var numsDict: [Int: Int] = [:] // Initialize an empty hashmap
for (index, num) in nums.enumerated() {
let complement = target - num // Calculate target value
if let complementIndex = numsDict[complement] {
return [complementIndex, index] // Return index
}
numsDict[num] = index // Add to hashmap
}
return [] // Return an empty array if no result
}
Step 4: Code Testing
Create test cases to verify that the implemented function works correctly.
let result = twoSum([2, 7, 11, 15], 9)
print(result) // [0, 1]
Debugging Process
Debugging is an essential step in the coding process.
Below is a case where we solved the problem using simple debugging methods:
1. Finding Logical Errors
When using a hashmap like the code above, multiple values can lead to the same target, which may give suboptimal results.
For example, it might return an invalid initial index, so we could add handling for that in the code.
2. Tracking Issues During Deployment
Before deploying code, document the expected results for various input values and
use that to identify discrepancies.
If the actual result differs from the expected result, it may indicate an issue with conditional statements or data structure configuration.
Exception Handling
Moreover, exception handling is a critical part that should not be overlooked.
It is important to provide appropriate responses when users input illegal values or an empty array.
We can add exception handling as follows:
func twoSum(_ nums: [Int], _ target: Int) -> [Int]? {
guard nums.count >= 2 else {
return nil // Return nil if input conditions are not met
}
var numsDict: [Int: Int] = [:]
for (index, num) in nums.enumerated() {
let complement = target - num
if let complementIndex = numsDict[complement] {
return [complementIndex, index]
}
numsDict[num] = index
}
return nil // Return nil if no result
}
Conclusion
Today, we solved the two-sum problem in Swift and learned the importance of debugging in the process.
To solve a problem, it is essential not just to write code but to examine the flow and logic through debugging.
Utilizing debugging in the process of solving algorithmic problems can lead to more efficient solutions.
I encourage you to practice debugging techniques while solving various problems.