Two Pointers Problem Solving

Use two pointers when problems involve sorted arrays, pairs, windows, or palindromes. Start pointers strategically, then move based on a deterministic rule to shrink search space in linear time.

Detect Pattern
Pairs / sorted / window
L ... R
Initialize
Left/right or slow/fast
Move by Rule
sum < target, move left
Pattern -> Pointers -> Movement Rule -> O(n)
Two-pointers workflow

Two Pointers Problem Solving

Learn when and how to apply two pointers for pair and window-style problems.
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1. Recognize the Pattern

Use this for sorted pair checks, palindrome validation, and sliding constraints.
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2. Initialize Pointers

Set left/right or slow/fast pointers depending on the problem structure.
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3. Define Movement Rules

Move pointers deterministically from comparisons to avoid brute-force nested loops.
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4. Validate Complexity

You usually visit each index once, giving O(n) time and O(1) extra space.
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Interactive Practice

Verify core complexity intuition for two-pointer solutions.
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Two Pointers in Code

Sample implementation for sorted two-sum with left/right pointers.

twoSumSorted.ts
function twoSumSorted(nums: number[], target: number): number[] {
  let left = 0;
  let right = nums.length - 1;

  while (left < right) {
    const sum = nums[left] + nums[right];

    if (sum === target) return [left, right];
    if (sum < target) left++;
    else right--;
  }

  return [];
}
Two pointers with deterministic movement rules
AlgoAnimator: Interactive Data Structures