Binary Search

Description

Given a sorted (in ascending order) integer array nums of n elements and a target value, write a function to search target in nums. If target exists, then return its index, otherwise return -1.

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

 

Note:

1. You may assume that all elements in nums are unique.
2. n will be in the range [1, 10000].
3. The value of each element in nums will be in the range [-9999, 9999].

Solution(javascript)

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number}
 */
const search = (nums, target) => {
  const aux = (low, high) => {
    if (low > high) {
      return -1
    }
    const middle = Math.floor((low + high) / 2)
    if (nums[middle] === target) {
      return middle
    } if (nums[middle] < target) {
      return aux(middle + 1, high)
    }
    return aux(low, middle - 1)
  }
  return aux(0, nums.length - 1)
}