sumZero.js

//                      MULTIPLE POINTERS
// Creating pointers or values that correspond to an index or position
// and move towards the beginning, end or middle based on a certain condition

// ===============================================================
// Write a function called sumZero which accepts a sorted array of
// integers. The function should find the first pair where the sum
// is 0. Return an array that includes both values that sum to zero
// or undefined if a pair does not exist.
// ===============================================================

// Time Complexity - O(N^2)
// Space Complexity - O(1)
// Brute force:
function sumZero(arr) {
  for (let i = 0; i < arr.length; i++) {
    for (let j = i + 1; j < arr.length; j++) {
      if (arr[i] + arr[j] === 0) {
        return [arr[i], arr[j]];
      }
    }
  }
}

// Time Complexity - O(N)
// Space Complexity - O(1)
// Refactor:
function sumZero(arr) {
  let left = 0;
  let right = arr.length - 1;
  while (left < right) {
    let sum = arr[left] + arr[right];
    if (sum === 0) {
      return [arr[left], arr[right]];
    } else if (sum > 0) {
      right--;
    } else {
      left++;
    }
  }
}