AI solution for JavaScript Coding Question on BFE.dev
50. search element right before target with Binary Search(possible duplicate array)

Solution:

We will use binary search to find the element right before first appearance of target number.

Here is the JavaScript code for the solution.

/** * @param {number[]} nums - sorted ascending array with duplicate numbers * @param {number} target * @return {number|undefined} */function binarySearchLastBefore(nums, target) {    let left = 0;  let right = nums.length - 1;  let index = -1;  while (left <= right) {      // middle index    const mid = Math.floor((left + right) / 2);        if (nums[mid] === target) {      // if mid index is target and mid index is not first element of array AND      // previous element to mid index is not target then return nums[mid-1]      if (mid > 0 && nums[mid-1] !== target) {        index = mid-1;        break;      } else {        // Otherwise try for the left half        right = mid-1;      }    } else if (nums[mid] < target) {      // Try for right half      left = mid+1;    } else {      // Try for left half      right = mid-1;    }  }  if (index !== -1) {    return nums[index];  }  return undefined;}