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6. Search Insert Position

easyAsked at Udemy

Find the index of a target or where it would insert — Udemy's classic binary-search check before course-catalog lookup questions.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Problem

Given a sorted array of distinct integers and a target value, return the index of the target. If absent, return the index where it would be inserted in order.

Constraints

  • 1 <= nums.length <= 10^4
  • -10^4 <= nums[i], target <= 10^4
  • nums sorted ascending, all distinct

Examples

Example 1

Input
nums=[1,3,5,6], target=5
Output
2

Example 2

Input
nums=[1,3,5,6], target=2
Output
1

Approaches

1. Linear scan

Walk left to right and return the first index >= target.

Time
O(n)
Space
O(1)
for (let i = 0; i < nums.length; i++) if (nums[i] >= target) return i;
return nums.length;

Tradeoff:

2. Binary search

Bisect by tightening lo/hi. When the loop ends, lo is the insertion index.

Time
O(log n)
Space
O(1)
function searchInsert(nums, target) {
  let lo = 0, hi = nums.length;
  while (lo < hi) {
    const mid = (lo + hi) >> 1;
    if (nums[mid] < target) lo = mid + 1;
    else hi = mid;
  }
  return lo;
}

Tradeoff:

Udemy-specific tips

Udemy interviewers will pivot to finding where a new course slot fits inside a sorted price tier — show clean binary-search bookkeeping with no off-by-one errors.

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Output

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