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6. Search Insert Position

easyAsked at SoFi

Binary search for the insertion point of a value — SoFi uses this to gauge fluency with sorted-array lookups in their loan-amortization tables.

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

Problem

Given a sorted array and a target, return the index if found; otherwise return the index where it would be inserted.

Constraints

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

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. Brute force

Linear scan for 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

Standard left-bound binary search. SoFi expects this and asks you to defend the invariant aloud.

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:

SoFi-specific tips

SoFi expects a clean half-open binary search and a verbal connection to looking up interest-rate tiers by FICO bucket in their pricing tables.

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Output

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