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Binary Search

Problem​

Given an array of integers nums which is sorted in ascending order, and an integer target, write a function to search target in nums. If target exists, then return its index. Otherwise, return -1.

You must write an algorithm with O(log n) runtime complexity.

 

Example 1:

Input: nums = [-1,0,3,5,9,12], target = 9
Output: 4
Explanation: 9 exists in nums and its index is 4

Example 2:

Input: nums = [-1,0,3,5,9,12], target = 2
Output: -1
Explanation: 2 does not exist in nums so return -1

 

Constraints:

  • 1 <= nums.length <= 104
  • -104 < nums[i], target < 104
  • All the integers in nums are unique.
  • nums is sorted in ascending order.

Solution​

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number}
 */
var search = function(nums, target) {
    let lo = 0;
    let hi = nums.length - 1;

    while (lo <= hi) {
        const mid = Math.floor((lo + hi) / 2);
        const val = nums[mid];
        if (val > target) {
            hi = mid - 1;
        } else if (val < target) {
            lo = mid + 1;
        } else {
            return mid;
        }
    }
    return -1;
};

Standard binary search implementation.