Skip to main content

6. Search Insert Position

easyAsked at Monzo

Find the index where a transaction amount should be inserted to keep an array sorted.

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) runtime complexity.

Constraints

  • 1 <= nums.length <= 10^4
  • 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 until you find a 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 binary search; return left on miss.

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:

Monzo-specific tips

Monzo expects lower-bound binary search to be muscle memory — it appears in their statement-merging and rate-table lookup code.

Solve it now

Free. No sign-up. Python and JavaScript run instantly in your browser.

Output

Press Run or Cmd+Enter to execute

Practice these live with InterviewChamp.AI

Drill Search Insert Position and other Monzo interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →