Two Pointers
This technique uses two pointers that move in the opposite direction. One pointer starts from the beginning while the other pointer starts from the end. The two pointers iterate across the input data until one or both of them satisfy the necessary condition.
How to Identify
- Data Structure Involves: Array, String, Linked List
- Question Type: Find a pair, a triplet, or even a subarray in arrays or Linked Lists.
Example
Two Sum II - Input Array Is Sorted
Given a 1-indexed array of integers numbers that is already sorted in non-decreasing order, find two numbers such that they add up to a specific target number. Let these two numbers be numbers[index1] and numbers[index2] where 1 <= index1 < index2 <= numbers.length.
Return the indices of the two numbers, index1 and index2, added by one as an integer array [index1, index2] of length 2.
The tests are generated such that there is exactly one solution. You may not use the same element twice.
Your solution must use only constant extra space.
Input: numbers = [2,7,11,15], target = 9
Output: [1,2]
Explanation: The sum of 2 and 7 is 9. Therefore, index1 = 1, index2 = 2. We return [1, 2].
function twoSum(numbers: number[], target: number): number[] {
let left = 0, right = numbers.length - 1
while(left < right){
const sum = numbers[left] + numbers[right]
if(sum === target) {
return [left + 1, right + 1]
} else if(sum < target){
left++
} else {
right--
}
}
return []
};
Related Problems
| Problems | Difficulty | |
|---|---|---|
| 1 | Squares of a Sorted Array | Easy |
| 2 | Two Sum II - Input Array Is Sorted | Medium |
| 3 | 3Sum | Medium |
| 4 | Container With Most Water | Medium |
| 5 | Trapping Rain Water | Hard |