Top 20 Two Pointers Interview Questions and Answers (2026)

1. Introduction to Two Pointers

Two pointers technique reduces O(n²) search to O(n). Below are 20 essential questions with full implementations in C++, Java, Python, and JavaScript.

2. Core Two Pointers Questions

Q1. Two Sum II — Sorted Array

cpp
vector<int> twoSum(vector<int>& numbers, int target) {
    int left = 0, right = numbers.size() - 1;
    while (left < right) {
        int sum = numbers[left] + numbers[right];
        if (sum == target) return {left + 1, right + 1};
        else if (sum < target) left++;
        else right--;
    }
    return {};
}

java
public int[] twoSum(int[] numbers, int target) {
    int left = 0, right = numbers.length - 1;
    while (left < right) {
        int sum = numbers[left] + numbers[right];
        if (sum == target) return new int[]{left + 1, right + 1};
        else if (sum < target) left++;
        else right--;
    }
    return new int[]{};
}

python
def twoSum(numbers: list, target: int) -> list:
    left, right = 0, len(numbers) - 1
    while left < right:
        total = numbers[left] + numbers[right]
        if total == target: return [left + 1, right + 1]
        elif total < target: left += 1
        else: right -= 1
    return []

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

Time Complexity: O(n) | Space Complexity: O(1)

3. Summary Table

Practice all two pointer problems on DSAMaster's practice platform.