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167. Two Sum II - Input Array Is Sorted 🔗

Date: Jun 02, 2024

Tags: two-pointers

Description

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.

Example 1:

      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].
      

Example 2:

      Input: numbers = [2,3,4], target = 6
      Output: [1,3]
      Explanation: The sum of 2 and 4 is 6. Therefore index1 = 1, index2 = 3. We return [1, 3].
      

Example 3:

      Input: numbers = [-1,0], target = -1
      Output: [1,2]
      Explanation: The sum of -1 and 0 is -1. Therefore index1 = 1, index2 = 2. We return [1, 2].
      

Constraints:

  • 2 <= numbers.length <= 3 * 104
  • -1000 <= numbers[i] <= 1000
  • numbers is sorted in non-decreasing order.
  • -1000 <= target <= 1000
  • The tests are generated such that there is exactly one solution.

Optimal

function twoSum(numbers: number[], target: number): number[] {
  let l = 0;
  let r = numbers.length - 1;

  while (l < r) {
    const sum = numbers[l] + numbers[r];

    if (sum === target) return [l + 1, r + 1];

    if (sum > target) r--;

    if (sum < target) l++;
  }

  throw new Error('No Two Sum solution');
}

export { twoSum };

Brute-Force

function twoSum(numbers: number[], target: number): number[] {
  let result: number[] = [];

  for (let x = 0; x < numbers.length; x++) {
    for (let y = x + 1; y < numbers.length; y++) {
      if (numbers[x] + numbers[y] === target) {
        result = [x + 1, y + 1];
        break;
      }
    }
  }

  return result;
}

export { twoSum };