Top 50 Array Problems
Arrays are the most fundamental data structure and appear in nearly every coding interview. Here are the most important array problems to master.
Essential Array Problems:
- Two Sum (with HashMap)
- Maximum Subarray Sum (Kadane's Algorithm)
- Best Time to Buy and Sell Stock
- Contains Duplicate
- Product of Array Except Self
- Maximum Product Subarray
- Find Minimum in Rotated Sorted Array
- Search in Rotated Sorted Array
- 3Sum
- Container With Most Water
- Trapping Rain Water
- Merge Intervals
- Insert Interval
- Non-overlapping Intervals
- Meeting Rooms / Meeting Rooms II
- Subarray Sum Equals K
- Majority Element (Moore's Voting)
- Spiral Matrix
- Rotate Image
- Set Matrix Zeroes
Strategies:
- Two-pointer technique for sorted arrays.
- HashMap for frequency and complement problems.
- Prefix sums for subarray queries.
- Sliding window for subarray/substring problems.
- Binary search on answer for optimization problems.
Let's implement one classic problem: Maximum Subarray Sum (Kadane)
public static int maxSubArray(int[] nums) {
int maxSoFar = nums[0];
int maxEndingHere = nums[0];
for (int i = 1; i < nums.length; i++) {
maxEndingHere = Math.max(nums[i], maxEndingHere + nums[i]);
maxSoFar = Math.max(maxSoFar, maxEndingHere);
}
return maxSoFar;
}
Two Minute Drill
- Master the 20+ essential array problems.
- Common techniques: two-pointer, sliding window, prefix sum, hash map, binary search.
- Practice with coding platforms (LeetCode, HackerRank).
- Focus on understanding patterns, not just memorizing solutions.
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