hasPairWithSum.js

/**
 * Find if there is a pair of numbers that sum to a given target value.
 *
 * Time Complexity:Quadratic time
 * nested loop so inefficient comparing of each i j to target
 * Space Complexity: O(N)
 * Optimal Time Complexity: O(N)
 *
 * @param {Array<number>} numbers - Array of numbers to search through
 * @param {number} target - Target sum to find
 * @returns {boolean} True if pair exists, false otherwise
 */

export function hasPairWithSum(numbers, target) {
	// for (let i = 0; i < numbers.length; i++) {
	//   for (let j = i + 1; j < numbers.length; j++) {
	//     if (numbers[i] + numbers[j] === target) {
	//       return true;
	//     }
	//   }
	// }

	const inventory = {};

	for (const num of numbers) {
		const needed = target - num;

		if (inventory[needed]) {
			return true;
		}

		inventory[num] = true;
	}
	return false;
}