167. Two Sum II - Input Array Is Sorted

Problem

Tags: Array, Two Pointers, Binary Search

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 * 10^4
• -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.

Code

JS

// 167. Two Sum II - Input Array Is Sorted (6/26/53718)
// Runtime: 72 ms (70.69%) Memory: 39.50 MB (94.29%) 

/**
 * @param {number[]} numbers
 * @param {number} target
 * @return {number[]}
 */
function twoSum(numbers, target) {
    const m = new Map();
    for (let i = 0; i < numbers.length; i++) {
        const n = numbers[i];
        if (m.has(n)) return [m.get(n), i + 1];
        m.set(target - n, i + 1);
    }
}