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6. Search Insert Position

easyAsked at Yelp

Binary-search a sorted array for an insert index — Yelp's gateway to the same lower-bound logic that places a new review at its correct rank-sorted slot.

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

Problem

Given a sorted array of distinct integers and a target, return the index of the target if found; otherwise return the index where it would be inserted in order. Must run in O(log n).

Constraints

  • 1 <= nums.length <= 10^4
  • -10^4 <= nums[i], target <= 10^4
  • nums is sorted ascending and 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 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 lower bound

Maintain [lo, hi] and shrink based on midpoint comparison.

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:

Yelp-specific tips

Yelp grades you on getting the lower-bound invariant exact — they'll ask how the same routine inserts a new business into a rank-sorted nearby-results array.

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Output

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