Leetcode #1060: Missing Element in Sorted Array
In this guide, we solve Leetcode #1060 Missing Element in Sorted Array in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
Given an integer array nums which is sorted in ascending order and all of its elements are unique and given also an integer k, return the kth missing number starting from the leftmost number of the array. Example 1: Input: nums = [4,7,9,10], k = 1 Output: 5 Explanation: The first missing number is 5.
Quick Facts
- Difficulty: Medium
- Premium: Yes
- Tags: Array, Binary Search
Intuition
The problem structure suggests a monotonic decision, which makes binary search a natural fit.
By halving the search space each step, we reach the answer efficiently.
Approach
Search either directly on a sorted array or on the answer space using a check function.
Each check is fast, and the logarithmic search keeps the overall runtime low.
Steps:
- Define the search bounds.
- Check the mid point condition.
- Narrow the bounds until convergence.
Example
Input: nums = [4,7,9,10], k = 1
Output: 5
Explanation: The first missing number is 5.
Python Solution
class Solution:
def missingElement(self, nums: List[int], k: int) -> int:
def missing(i: int) -> int:
return nums[i] - nums[0] - i
n = len(nums)
if k > missing(n - 1):
return nums[n - 1] + k - missing(n - 1)
l, r = 0, n - 1
while l < r:
mid = (l + r) >> 1
if missing(mid) >= k:
r = mid
else:
l = mid + 1
return nums[l - 1] + k - missing(l - 1)
Complexity
The time complexity is O(log n) or O(n log n). The space complexity is O(1).
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.