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6. Search Insert Position

easyAsked at Slack

Find the index where a target should be inserted in a sorted array.

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

Problem

Given a sorted array of distinct integers and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order. You must write an algorithm with O(log n) time complexity.

Constraints

  • 1 <= nums.length <= 10^4
  • nums contains distinct values sorted ascending

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 array until value >= 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

Standard lower-bound binary search. Return left after the loop.

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:

Slack-specific tips

Slack uses sorted ts arrays for channel timelines — they expect you to nail off-by-one edges (hi = nums.length, not length - 1).

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