LeetCode #164 — MEDIUM

Maximum Gap

Move from brute-force thinking to an efficient approach using array strategy.

The Problem

Problem Statement

Given an integer array nums, return the maximum difference between two successive elements in its sorted form. If the array contains less than two elements, return 0.

You must write an algorithm that runs in linear time and uses linear extra space.

Example 1:

Input: nums = [3,6,9,1]
Output: 3
Explanation: The sorted form of the array is [1,3,6,9], either (3,6) or (6,9) has the maximum difference 3.

Example 2:

Input: nums = [10]
Output: 0
Explanation: The array contains less than 2 elements, therefore return 0.

Constraints:

1 <= nums.length <= 10⁵
0 <= nums[i] <= 10⁹

Step 01

Brute Force Baseline

Problem summary: Given an integer array nums, return the maximum difference between two successive elements in its sorted form. If the array contains less than two elements, return 0. You must write an algorithm that runs in linear time and uses linear extra space.

Baseline thinking

Start with the most direct exhaustive search. That gives a correctness anchor before optimizing.

Pattern signal: Array

Example 1

[3,6,9,1]

Example 2

[10]

Core Insight

What unlocks the optimal approach

No official hints in dataset. Start from constraints and look for a monotonic or reusable state.

Interview move: turn each hint into an invariant you can check after every iteration/recursion step.

Step 03

Algorithm Walkthrough

Iteration Checklist

Define state (indices, window, stack, map, DP cell, or recursion frame).
Apply one transition step and update the invariant.
Record answer candidate when condition is met.
Continue until all input is consumed.

Use the first example testcase as your mental trace to verify each transition.

Step 04

Edge Cases

Minimum Input

Single element / shortest valid input

Validate boundary behavior before entering the main loop or recursion.

Duplicates & Repeats

Repeated values / repeated states

Decide whether duplicates should be merged, skipped, or counted explicitly.

Extreme Constraints

Upper-end input sizes

Re-check complexity target against constraints to avoid time-limit issues.

Invalid / Corner Shape

Empty collections, zeros, or disconnected structures

Handle special-case structure before the core algorithm path.

Step 05

Full Annotated Code

Source-backed implementations are provided below for direct study and interview prep.

// Accepted solution for LeetCode #164: Maximum Gap
class Solution {
    public int maximumGap(int[] nums) {
        int n = nums.length;
        if (n < 2) {
            return 0;
        }
        int inf = 0x3f3f3f3f;
        int mi = inf, mx = -inf;
        for (int v : nums) {
            mi = Math.min(mi, v);
            mx = Math.max(mx, v);
        }
        int bucketSize = Math.max(1, (mx - mi) / (n - 1));
        int bucketCount = (mx - mi) / bucketSize + 1;
        int[][] buckets = new int[bucketCount][2];
        for (var bucket : buckets) {
            bucket[0] = inf;
            bucket[1] = -inf;
        }
        for (int v : nums) {
            int i = (v - mi) / bucketSize;
            buckets[i][0] = Math.min(buckets[i][0], v);
            buckets[i][1] = Math.max(buckets[i][1], v);
        }
        int prev = inf;
        int ans = 0;
        for (var bucket : buckets) {
            if (bucket[0] > bucket[1]) {
                continue;
            }
            ans = Math.max(ans, bucket[0] - prev);
            prev = bucket[1];
        }
        return ans;
    }
}

// Accepted solution for LeetCode #164: Maximum Gap
func maximumGap(nums []int) int {
	n := len(nums)
	if n < 2 {
		return 0
	}
	inf := 0x3f3f3f3f
	mi, mx := inf, -inf
	for _, v := range nums {
		mi = min(mi, v)
		mx = max(mx, v)
	}
	bucketSize := max(1, (mx-mi)/(n-1))
	bucketCount := (mx-mi)/bucketSize + 1
	buckets := make([][]int, bucketCount)
	for i := range buckets {
		buckets[i] = []int{inf, -inf}
	}
	for _, v := range nums {
		i := (v - mi) / bucketSize
		buckets[i][0] = min(buckets[i][0], v)
		buckets[i][1] = max(buckets[i][1], v)
	}
	ans := 0
	prev := inf
	for _, bucket := range buckets {
		if bucket[0] > bucket[1] {
			continue
		}
		ans = max(ans, bucket[0]-prev)
		prev = bucket[1]
	}
	return ans
}

# Accepted solution for LeetCode #164: Maximum Gap
class Solution:
    def maximumGap(self, nums: List[int]) -> int:
        n = len(nums)
        if n < 2:
            return 0
        mi, mx = min(nums), max(nums)
        bucket_size = max(1, (mx - mi) // (n - 1))
        bucket_count = (mx - mi) // bucket_size + 1
        buckets = [[inf, -inf] for _ in range(bucket_count)]
        for v in nums:
            i = (v - mi) // bucket_size
            buckets[i][0] = min(buckets[i][0], v)
            buckets[i][1] = max(buckets[i][1], v)
        ans = 0
        prev = inf
        for curmin, curmax in buckets:
            if curmin > curmax:
                continue
            ans = max(ans, curmin - prev)
            prev = curmax
        return ans

// Accepted solution for LeetCode #164: Maximum Gap
struct Solution;

impl Solution {
    fn maximum_gap(mut nums: Vec<i32>) -> i32 {
        let n = nums.len();
        nums.sort_unstable();
        let mut res = 0;
        for i in 1..n {
            res = res.max(nums[i] - nums[i - 1]);
        }
        res
    }
}

#[test]
fn test() {
    let nums = vec![3, 6, 9, 1];
    let res = 3;
    assert_eq!(Solution::maximum_gap(nums), res);
}

// Accepted solution for LeetCode #164: Maximum Gap
// Auto-generated TypeScript example from java.
function exampleSolution(): void {
}
// Reference (java):
// // Accepted solution for LeetCode #164: Maximum Gap
// class Solution {
//     public int maximumGap(int[] nums) {
//         int n = nums.length;
//         if (n < 2) {
//             return 0;
//         }
//         int inf = 0x3f3f3f3f;
//         int mi = inf, mx = -inf;
//         for (int v : nums) {
//             mi = Math.min(mi, v);
//             mx = Math.max(mx, v);
//         }
//         int bucketSize = Math.max(1, (mx - mi) / (n - 1));
//         int bucketCount = (mx - mi) / bucketSize + 1;
//         int[][] buckets = new int[bucketCount][2];
//         for (var bucket : buckets) {
//             bucket[0] = inf;
//             bucket[1] = -inf;
//         }
//         for (int v : nums) {
//             int i = (v - mi) / bucketSize;
//             buckets[i][0] = Math.min(buckets[i][0], v);
//             buckets[i][1] = Math.max(buckets[i][1], v);
//         }
//         int prev = inf;
//         int ans = 0;
//         for (var bucket : buckets) {
//             if (bucket[0] > bucket[1]) {
//                 continue;
//             }
//             ans = Math.max(ans, bucket[0] - prev);
//             prev = bucket[1];
//         }
//         return ans;
//     }
// }

Step 06

Interactive Study Demo

Use this to step through a reusable interview workflow for this problem.

Custom checkpoints (one per line)

Press Step or Run All to begin.

Step 07

Complexity Analysis

Time

O(n)

Space

O(1)

Approach Breakdown

BRUTE FORCE

O(n²) time

O(1) space

Two nested loops check every pair or subarray. The outer loop fixes a starting point, the inner loop extends or searches. For n elements this gives up to n²/2 operations. No extra space, but the quadratic time is prohibitive for large inputs.

OPTIMIZED

O(n) time

O(1) space

Most array problems have an O(n²) brute force (nested loops) and an O(n) optimal (single pass with clever state tracking). The key is identifying what information to maintain as you scan: a running max, a prefix sum, a hash map of seen values, or two pointers.

Shortcut: If you are using nested loops on an array, there is almost always an O(n) solution. Look for the right auxiliary state.

Coach Notes

Common Mistakes

Review these before coding to avoid predictable interview regressions.

Off-by-one on range boundaries

Wrong move: Loop endpoints miss first/last candidate.

Usually fails on: Fails on minimal arrays and exact-boundary answers.

Fix: Re-derive loops from inclusive/exclusive ranges before coding.