completed comeptitive coding - 2#1190
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Pull request overview
Adds a Java solution for the classic “Two Sum” problem as part of the competitive coding exercises in this repository.
Changes:
- Added
twoSumimplementation using aHashMaplookup strategy. - Added header comments describing complexity and approach.
Reviewed changes
Copilot reviewed 1 out of 2 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
| twosum.java | Introduces a Two Sum solution; needs minor adjustments to be self-contained Java and to simplify redundant logic. |
| Problem1.java | Listed in the PR prompt, but the file wasn’t present in the repository snapshot provided to the reviewer, so changes could not be verified here. |
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| // Did this code successfully run on Leetcode : yes | ||
| // Any problem you faced while coding this : difficult to come up with the approach of using hashmap to store the values and their indices. | ||
| // Your code here along with comments explaining your approach: hashmap is used to store the values and their indices. In the first loop, we store all the values and their indices in the hashmap. In the second loop, we check if the complement of the current value (target - current value) exists in the hashmap and if it does, we return the indices of the two values. | ||
| class Solution { |
| HashMap<Integer, Integer> map = new HashMap<>(); | ||
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| for(int i = 0; i < nums.length; i++) { | ||
| map.put(nums[i], i); | ||
| } | ||
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| for (int i = 0; i < nums.length; i++) { | ||
| int cmp = target - nums[i]; | ||
| if (map.containsKey(cmp) && map.get(cmp) != i) { | ||
| return new int[]{map.get(cmp),i}; | ||
| } | ||
| map.put(nums[i], i); | ||
| } | ||
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| return new int[]{}; |
| // Space Complexity : O(n) | ||
| // Did this code successfully run on Leetcode : yes | ||
| // Any problem you faced while coding this : difficult to come up with the approach of using hashmap to store the values and their indices. | ||
| // Your code here along with comments explaining your approach: hashmap is used to store the values and their indices. In the first loop, we store all the values and their indices in the hashmap. In the second loop, we check if the complement of the current value (target - current value) exists in the hashmap and if it does, we return the indices of the two values. |
Two Sum (twosum.java)Strengths:
Areas for Improvement:
Minor Optimization: for (int i = 0; i < nums.length; i++) {
int cmp = target - nums[i];
if (map.containsKey(cmp)) {
return new int[]{map.get(cmp), i};
}
map.put(nums[i], i);
}This single-pass approach is more efficient as it avoids the redundant map population. VERDICT: PASS Interview Problem: 0-1 Knapsack ProblemThe student appears to have submitted code for the wrong problem entirely. This could indicate:
If this was intentional for a different assignment, the Two Sum solution itself is well-written with clear explanations. However, for the 0-1 Knapsack Problem specifically, the student needs to implement a dynamic programming approach using a 2D array where dp[i][w] represents the maximum value achievable with the first i items and a capacity of w. For the Two Sum solution, the redundant HashMap population in the second loop could be removed to slightly improve efficiency. VERDICT: NEEDS_IMPROVEMENT |
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