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Mastering the Two Pointer Technique

Learn when and how to use the two pointer pattern to solve array problems efficiently.

January 22, 20245 min read

Mastering the Two Pointer Technique

The two pointer technique is a pattern that uses two pointers to iterate through a data structure. It's incredibly versatile and efficient.

When to Use Two Pointers

Sorted arrays
Finding pairs with specific conditions
In-place array modifications
Palindrome problems

Pattern Variations

Opposite Direction

function twoSum(arr, target) {
  let left = 0, right = arr.length - 1;
  while (left < right) {
    const sum = arr[left] + arr[right];
    if (sum === target) return [left, right];
    if (sum < target) left++;
    else right--;
  }
  return [-1, -1];
}

Same Direction (Fast/Slow)

function removeDuplicates(arr) {
  if (arr.length === 0) return 0;
  let slow = 0;
  for (let fast = 1; fast < arr.length; fast++) {
    if (arr[fast] !== arr[slow]) {
      slow++;
      arr[slow] = arr[fast];
    }
  }
  return slow + 1;
}

Classic Problems

Container With Most Water - Opposite direction
Remove Duplicates - Same direction
Three Sum - Two pointers + iteration

Practice these patterns until they become second nature!

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