Array Algorithms

Master essential array problem-solving patterns and techniques

Two Pointer Technique: Find Pair with Sum

Target Sum:

Left Pointer: 0

Right Pointer: 8

Sliding Window: Maximum Sum Subarray

Window Size:

Current window sum: 8 | Maximum sum found: 0

Essential Array Algorithms

Two Pointer Technique

Use two pointers moving towards each other or in the same direction

Time Complexity:O(n)

Space Complexity:O(1)

Common Use Cases:

Finding pairs with target sum
Palindrome checking
Removing duplicates
Merging sorted arrays

Algorithm Pseudocode:

Pseudocode

1ALGORITHM: Two Pointer Sum
2INPUT: sorted_array[], target_sum
3OUTPUT: pair indices or -1
4 
5BEGIN
61. left = 0
72. right = array.length - 1
83. 
94. WHILE left < right DO
105.     sum = array[left] + array[right]
116.     IF sum == target_sum THEN
127.         RETURN (left, right)
138.     ELSE IF sum < target_sum THEN
149.         left = left + 1
1510.    ELSE
1611.        right = right - 1
1712.    END IF
1813. END WHILE
1914. 
2015. RETURN -1  // No pair found
21END

C++ Implementation:

// Two Pointer Sum in C++
vector<int> twoSum(vector<int>& nums, int target) {
    int left = 0, right = nums.size() - 1;
    
    while (left < right) {
        int sum = nums[left] + nums[right];
        if (sum == target) {
            return {left, right};
        } else if (sum < target) {
            left++;
        } else {
            right--;
        }
    }
    return {-1, -1}; // Not found
}

Practice Problems

Beginner Problems

Two Sum (Sorted Array)

Find two numbers that add up to target

Maximum Sum Subarray (Size K)

Find maximum sum of any subarray of size K

Range Sum Queries

Answer multiple range sum queries efficiently

Intermediate Problems

3Sum Problem

Find all unique triplets that sum to zero

Longest Substring (No Repeats)

Find longest substring with unique characters

Subarray Sum Equals K

Count subarrays with sum equal to K

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