Java Solution for LeetCode's Path Sum Problem

🚀 Day 92 – #100DaysOfCode Qn. Combination Sum III Today I worked on the Combination Sum III problem using recursion and backtracking in Java. 🔹 Problem Summary: Find all possible combinations of k numbers that add up to n, using numbers 1–9 only once. 🔹 My Approach: Used recursion to explore all possible number combinations. Maintained a running sum and a temporary list. When the sum equals n and the list size equals k, the combination is added to the result. Used a HashSet to avoid duplicate combinations. 🔹 Key Learning: This problem helped me strengthen my understanding of: Backtracking Recursive decision trees Managing state during recursion (adding/removing elements) 📌 Next Goal: Optimize the solution further by avoiding the HashSet and pruning unnecessary recursive calls. #Day92 #LeetCode #DSA #Java #Recursion #Backtracking #CodingJourney

Day 45 of #100DaysOfLeetCode 💻✅ Solved Simple #268. Missing Number problem in Java. Approach: • Calculated the expected sum of numbers from 0 to n using the formula n(n+1)/2 • Traversed the array and calculated the actual sum of the elements • Subtracted the actual sum from the expected sum • The difference gives the missing number in the array Performance: ✓ Runtime: 0 ms (Beats 100% submissions) 🚀 ✓ Memory: 47.60 MB (Beats 29.84% submissions) Key Learning: ✓ Practiced using mathematical formulas to simplify problems ✓ Learned how sum comparison can help find a missing element efficiently ✓ Strengthened problem-solving skills with arrays Learning one problem every single day 🚀 #Java #LeetCode #DSA #Arrays #ProblemSolving #CodingJourney #100DaysOfCode

Day 44 of #100DaysOfLeetCode 💻✅ Solved Very Simple #169. Majority Element problem in Java. Approach: • Sorted the given array using Arrays.sort() • Observed that the majority element appears more than n/2 times • After sorting, the majority element will always be present at index n/2 • Returned the element at nums[n/2] Performance: ✓ Runtime: 7 ms (Beats 42.86% submissions) ✓ Memory: 55.96 MB (Beats 16.21% submissions) Key Learning: ✓ Understood how sorting can help identify the majority element ✓ Learned the property that the majority element always occupies the middle position after sorting ✓ Practiced array manipulation and problem solving in Java Learning one problem every single day 🚀 #Java #LeetCode #DSA #Arrays #ProblemSolving #CodingJourney #100DaysOfCode

Day 63 of #100DaysOfLeetCode 💻✅ Solved #2085. Count Common Words With One Occurrence problem in Java. Approach: • Iterated through each word in the first array • Avoided duplicate checks by ensuring each word is processed only once • Counted occurrences of the current word in both arrays • If the word appears exactly once in both arrays, incremented the result • Returned the final count Performance: ✓ Runtime: 88 ms (Beats 7.45% submissions) ✓ Memory: 46.06 MB (Beats 93.07% submissions) Key Learning: ✓ Practiced handling duplicates and frequency counting ✓ Improved understanding of string comparison in arrays ✓ Learned importance of optimizing nested loop solutions Learning one problem every single day 🚀 #Java #LeetCode #DSA #Strings #Arrays #ProblemSolving #CodingJourney #100DaysOfCode

Day 46 of #100DaysOfLeetCode 💻✅ Solved #374. Guess Number Higher or Lower problem in Java. Approach: • Used Binary Search to efficiently guess the number. • Calculated mid using low + (high - low) / 2 to avoid overflow. • Used the guess(mid) API to check if the number is higher, lower, or correct. • Updated the search range accordingly until the number was found. Performance: ✓ Runtime: 0 ms (Beats 100% submissions) 🚀 ✓ Memory: 41.68 MB (Beats 97.84% submissions) Key Learning: ✓ Practiced implementing binary search on a real problem ✓ Learned how to safely calculate mid to prevent integer overflow ✓ Strengthened problem-solving skills with search algorithms Learning one problem every single day 🚀 #Java #LeetCode #DSA #BinarySearch #ProblemSolving #CodingJourney #100DaysOfCode

Day 66 of #100DaysOfLeetCode 💻✅ Solved #3427. Sum of Variable Length Subarrays problem in Java. Approach: • Iterated through each index of the array • Determined the starting index using i - nums[i] • Ensured the start index does not go below 0 • Calculated sum of elements from start to current index i • Added each subarray sum to the total Performance: ✓ Runtime: 1 ms (Beats 99.90% submissions) ✓ Memory: 45.22 MB (Beats 56.30% submissions) Key Learning: ✓ Practiced handling variable-length subarrays ✓ Improved understanding of index-based range calculations ✓ Strengthened nested loop logic for array problems Learning one problem every single day 🚀 #Java #LeetCode #DSA #Arrays #PrefixSum #ProblemSolving #CodingJourney #100DaysOfCode

Day 64 of #100DaysOfLeetCode 💻✅ Solved #724. Find Pivot Index problem in Java. Approach: • Calculated the total sum of the array • Maintained a variable left to track left sum • For each index, computed right sum as total - left - nums[i] • Compared left and right sums • If both are equal, returned the index as pivot • Updated left sum by adding current element Performance: ✓ Runtime: 1 ms (Beats 98.68% submissions) 🚀 ✓ Memory: 47.58 MB (Beats 32.00% submissions) Key Learning: ✓ Learned prefix sum technique for efficient calculations ✓ Practiced reducing time complexity from O(n²) to O(n) ✓ Strengthened understanding of array traversal and sum logic Learning one problem every single day 🚀 #Java #LeetCode #DSA #Arrays #PrefixSum #ProblemSolving #CodingJourney #100DaysOfCode

Day 51 of #100DaysOfLeetCode 💻✅ Solved #217. Contains Duplicate problem in Java. Approach: • Sorted the array using Arrays.sort() • Traversed the array starting from index 1 • Compared each element with its previous element • If any two adjacent elements are equal, returned true • If no duplicates are found, returned false Performance: ✓ Runtime: 24 ms (Beats 26.49% submissions) ✓ Memory: 76.56 MB (Beats 96.73% submissions) Key Learning: ✓ Practiced sorting-based approach for detecting duplicates ✓ Learned how sorting helps bring duplicate elements together ✓ Strengthened understanding of array traversal techniques Learning one problem every single day 🚀 #Java #LeetCode #DSA #Arrays #ProblemSolving #CodingJourney #100DaysOfCode

Day 47 of #100DaysOfLeetCode 💻✅ Solved #101. Symmetric Tree problem in Java. Approach: • Used recursion to compare the left and right subtrees of the root • If both nodes are null, the tree is symmetric at that level • If one node is null and the other is not, the tree is not symmetric • Compared the values of both nodes • Recursively checked left.left with right.right and left.right with right.left to verify mirror structure Performance: ✓ Runtime: 0 ms (Beats 100% submissions) ✓ Memory: 43.62 MB (Beats 48.60% submissions) Key Learning: ✓ Practiced mirror comparison in binary trees ✓ Learned how recursion can verify symmetry between two subtrees ✓ Strengthened understanding of tree traversal and structural comparison Learning one problem every single day 🚀 #Java #LeetCode #DSA #BinaryTrees #ProblemSolving #CodingJourney #100DaysOfCode

Day 67 of #100DaysOfLeetCode 💻✅ Solved #91. Decode Ways problem in Java. Approach: • Checked if the input string is empty or starts with '0' • Initialized a DP array to store number of ways to decode up to each index • Used dp[i] = dp[i-1] if single digit is valid (1–9) • Added dp[i-2] if two-digit number is valid (10–26) • Returned dp[n] as the total number of decoding ways Performance: ✓ Runtime: 1 ms (Beats 99.90%) ✓ Memory: 41.5 MB (Beats 55%) Key Learning: ✓ Practiced dynamic programming with strings ✓ Strengthened understanding of single vs double digit constraints ✓ Reinforced how to build DP solutions incrementally Learning one problem every single day 🚀 #Java #LeetCode #DSA #DynamicProgramming #ProblemSolving #CodingJourney #100DaysOfCode