How do I identify the longest sequential prefix?

To identify the longest sequential prefix, iterate through the array and check if nums[i] = nums[i-1] + 1. Stop when this condition is violated.

What is the significance of the sum of the sequential prefix?

The sum of the longest sequential prefix is used to determine the smallest integer that is greater than or equal to this sum but not present in the array.

What are the challenges with finding missing integers?

The main challenge is efficiently finding missing integers, especially when the array can have elements that span a large range.

Can this problem be solved without using a hash table?

Yes, it's possible to solve the problem using sorting and array scanning without a hash table. However, a hash table is usually more efficient for lookups.

How does GhostInterview assist with this problem?

GhostInterview offers tailored hints on array scanning, hash lookups, and efficient ways to identify missing integers, making the problem-solving process smoother.

#2996

Easy

auto_awesome数组·哈希·扫描

LeetCode 题解工作台

大于等于顺序前缀和的最小缺失整数

给你一个下标从 0 开始的整数数组 nums 。如果一个前缀 nums[0..i] 满足对于 1 的所有元素都有 nums[j] = nums[j - 1] + 1 ，那么我们称这个前缀是一个顺序前缀。特殊情况是，只包含 nums[0] 的前缀也是一个顺序前缀。请你返回 nums 中没有…

数组哈希表排序

题目描述

给你一个下标从 0 开始的整数数组 nums 。

如果一个前缀 nums[0..i] 满足对于 1 <= j <= i 的所有元素都有 nums[j] = nums[j - 1] + 1 ，那么我们称这个前缀是一个 顺序前缀 。特殊情况是，只包含 nums[0] 的前缀也是一个 顺序前缀 。

请你返回 nums 中没有出现过的最小整数 x ，满足 x 大于等于最长顺序前缀的和。

示例 1：

输入：nums = [1,2,3,2,5]
输出：6
解释：nums 的最长顺序前缀是 [1,2,3] ，和为 6 ，6 不在数组中，所以 6 是大于等于最长顺序前缀和的最小整数。

示例 2：

输入：nums = [3,4,5,1,12,14,13]
输出：15
解释：nums 的最长顺序前缀是 [3,4,5] ，和为 12 ，12、13 和 14 都在数组中，但 15 不在，所以 15 是大于等于最长顺序前缀和的最小整数。

提示：

1 <= nums.length <= 50
1 <= nums[i] <= 50

lightbulb

解题思路

方法一：模拟 + 哈希表

我们先求出数组 $nums$ 的最长顺序前缀和 $s$ ，然后从 $s$ 开始枚举整数 $x$ ，如果 $x$ 不在数组 $nums$ 中，那么 $x$ 就是答案。这里我们可以用哈希表来快速判断一个整数是否在数组 $nums$ 中。

时间复杂度 $O(n)$ ，空间复杂度 $O(n)$ 。其中 $n$ 是数组 $nums$ 的长度。

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class Solution:
    def missingInteger(self, nums: List[int]) -> int:
        s, j = nums[0], 1
        while j < len(nums) and nums[j] == nums[j - 1] + 1:
            s += nums[j]
            j += 1
        vis = set(nums)
        for x in count(s):
            if x not in vis:
                return x

speed

复杂度分析

指标	值
时间	Depends on the final approach
空间	Depends on the final approach

psychology

面试官常问的追问

外企场景

question_mark
The candidate correctly identifies the sequential prefix and calculates its sum.
question_mark
The candidate demonstrates a clear approach to finding missing integers using efficient data structures.
question_mark
The candidate optimizes the problem-solving process by considering edge cases and handling array traversal effectively.

warning

常见陷阱

外企场景

error
Incorrectly identifying the longest sequential prefix due to faulty array traversal.
error
Failing to calculate the sum of the sequential prefix properly.
error
Not considering how to find missing integers efficiently, either by skipping hash table usage or miscalculating the sum.

swap_horiz

进阶变体

外企场景

arrow_right_alt
Consider implementing the solution with sorting and scanning instead of using hash tables.
arrow_right_alt
Test the problem with an array of maximum size (50) to evaluate the solution's efficiency.
arrow_right_alt
Investigate edge cases with minimal input (i.e., a single element array).

help

常见问题

外企场景

继续练习

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