Binary Search

Problem Description

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 (JavaScript)

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number}
 */
var search = function(nums, target) {
    const searchTarget = (nums, target, left, right) => {
        if (left > right) {
            return -1;
        }
        const mid = left+Math.floor((right-left)/2);
        if (nums[mid] === target) {
            return mid;
        } else if (nums[mid] < target) {
            return searchTarget(nums, target, mid+1, right);
        } else {
            return searchTarget(nums, target, left, mid-1);
        }
    };
    return searchTarget(nums, target, 0, nums.length-1);
};