Add: Two Sum (C++)

[rishanmenezes]

PR Title Format: 1. Two Sum.cpp

Intuition

The "Two Sum" problem asks us to find two numbers in an array that add up to a specific target. A brute-force approach would involve checking every possible pair, which is O(n^2). To optimize this, we can use a hash map (unordered_map in C++) to store numbers we've already seen along with their indices. This allows us to quickly check if the complement (target - current number) exists in the map.

Approach

1. Initialize an unordered_map called numMap to store numbers and their indices.
2. Iterate through the input array nums with an index i .
3. For each number nums[i] , calculate the complement needed to reach the target (i.e., target - nums[i] ).
4. Check if the complement exists as a key in numMap .
   • If it does, we have found the two numbers. Return the index of the complement (stored in numMap ) and the current index i .
5. If the complement is not found, add the current number nums[i] and its index i to the numMap .
6. If the loop completes without finding a pair (which shouldn't happen based on the problem constraints, as a solution is guaranteed), return an empty vector or handle as appropriate.

Code Solution (C++)

#include <vector>
#include <unordered_map>

class Solution {
public:
    std::vector<int> twoSum(std::vector<int>& nums, int target) {
        std::unordered_map<int,  int> numMap;
        int n = nums.size();

        for (int i = 0; i < n; ++i) 
        {
            int complement = target 
            - nums[i];
            if (numMap.count
            (complement)) {
                return {numMap
                [complement], i};
            }
            numMap[nums[i]] = i;
        }

        return {}; // Should not 
        happen based on problem 
        constraints
    }
};

Related Issues

#193

By submitting this PR, I confirm that:

• This is my original work not totally AI generated
• I have tested the solution thoroughly on leetcode
• I have maintained proper PR description format
• This is a meaningful contribution, not spam

Summary by Sourcery

New Features:

• Implement Two Sum solution in C++ leveraging a hash map for complement lookup.

[sourcery-ai]

Reviewer's Guide

Introduces a linear-time C++ implementation for the Two Sum problem by leveraging an unordered_map to track previously seen numbers and their indices for constant-time complement lookups.

Class diagram for the new Solution class (Two Sum)

classDiagram
class Solution {
  +std::vector<int> twoSum(std::vector<int>& nums, int target)
}

Loading

File-Level Changes

Change	Details	Files
Add a hash map-optimized Two Sum algorithm	Initialize an unordered_map to map values to their indices Iterate over the input vector and compute the complement for each element Check and return the stored index when the complement is found Insert the current element and its index into the map when no match is found Include an unreachable empty-vector fallback return	1. Two Sum.cpp

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[sourcery-ai]

Hey there - I've reviewed your changes - here's some feedback:

• Consider using auto it = numMap.find(complement) and checking it != end() to avoid two hash lookups (count + operator[]).
• Reserve space in numMap (numMap.reserve(nums.size())) before the loop to reduce rehashing overhead for large inputs.
• Use size_t for the loop index and n (instead of int) to match nums.size() return type and avoid type mismatches.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider using auto it = numMap.find(complement) and checking it != end() to avoid two hash lookups (count + operator[]).
- Reserve space in numMap (numMap.reserve(nums.size())) before the loop to reduce rehashing overhead for large inputs.
- Use size_t for the loop index and n (instead of int) to match nums.size() return type and avoid type mismatches.

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[SjxSubham]

@rishanmenezes raise an ISSUE as well,,, as it;'s not present at the existing ISSUE list,,,

[rishanmenezes]

@rishanmenezes raise an ISSUE as well,,, as it;'s not present at the existing ISSUE list,,,

i have raised an issue as well

[SjxSubham]

@rishanmenezes raise an ISSUE as well,,, as it;'s not present at the existing ISSUE list,,,

i have raised an issue as well

1. make the chnages which i mentioned on that issue 1. Two Sum (C++) #193
2. as well as Star the repo ⭐
3. Rename the PR title/PR name with Proper format Problem no. Problem name.cpp